Hi everyone, this is Zulaikha from Edureka,
and I welcome you to this session
on Artificial Intelligence full course.
In this video, I'll be covering
all the domains and the concepts
involved under the umbrella of artificial intelligence,
and I will also be showing you a couple of use cases
and practical implementations by using Python.
So there's a lot to cover in this session,
and let me quickly run you through today's agenda.
So we're gonna begin the session
by understanding the history of artificial intelligence
and how it cam into existence.
We'll follow this by looking at
why we're talking about artificial intelligence now,
why has it gotten so famous right now.
Then we'll look at what exactly is artificial intelligence.
We'll discuss the applications of artificial intelligence,
after which we'll discuss the basics of AI
where in we'll understand
the different types of artificial intelligence.
We'll follow this by understanding
the different programming languages
that can be used to study AI.
And we'll understand why we're gonna choose Python.
Alright, I'll introduce you to Python.
And then we'll move on and discuss machine learning.
Here we'll discuss the different types of machine learning,
the different algorithms involved in machine learning,
which include classification algorithms,
regression algorithms, clustering,
and association algorithms.
To make you understand machine learning better,
we'll run a couple of demos
wherein we'll see how machine learning algorithms
are used to solve real world problems.
After that, we'll discuss
the limitations of machine learning
and why deep learning is needed.
I'll introduce you to the deep learning concept,
what are neurons, perceptrons,
multiple layer perceptrons and so on.
We'll discuss the different types of neural networks,
and we'll also look at what exactly back propagation is.
Apart from this, we'll be running a demo
to understand deep learning in more depth.
And finally we'll move onto the next module,
which is natural language processing.
On the natural language processing,
we'll try to understand what is text mining,
the difference between text mining in NLP,
what are the different terminologies in NLP,
and we'll end the session by looking at
the practical implementation of NLP using Python, alright.
So guys, there's a lot to cover in today's session.
Also, if you want to stay updated
about the recent technologies,
and would like to learn more about the training technology,
make sure you subscribe to our YouTube channel
to never miss out on such sessions.
So let's move ahead and take a look at our first topic
which is history of artificial intelligence.
So guys, the concept of artificial intelligence
goes back to the classical ages.
Under Greek mythology,
the concept of machines and mechanical men
were well thought of.
So, an example of this is Talos.
I don't know how many of you have heard of this.
Talos was a giant animated bronze warrior
who was programmed to guard the island of Crete.
Now these are just ideas.
Nobody knows if this was actually implemented,
but machine learning and AI were thought of long ago.
Now let's get back to the 19th century.
Now 1950 was speculated to be
one of the most important years
for the introduction of artificial intelligence.
In 1950, Alan Turing published a paper
in which he speculated about the possibility
of creating machines that think.
So he created what is known as the Turing test.
This test is basically used to determine
whether or not a computer can think intelligently
like a human being.
He noted that thinking is difficult to define
and devised his famous Turing test.
So, basically, if a machine can carry out a conversation
that was indistinguishable
from a conversation with a human being,
it was reasonable to say that the machine is thinking,
meaning that the machine will pass the Turing test.
Now, unfortunately, up to this date,
we haven't found a machine that has fully cleared
the Turing test.
So, the Turing test was actually the first serious proposal
in the philosophy of artificial intelligence.
Followed by this was the era of 1951.
This was also known as the game AI.
So in 1951, by using the Ferranti Mark 1 machine
of the University of Manchester,
a computer scientist known as Christopher Strachey
wrote a checkers program.
And at the same time,
a program was written for chess as well.
Now, these programs were later improved and redone,
but this was the first attempt
at creating programs that could play chess
or that would compete with humans in playing chess.
This is followed by the year 1956.
Now, this is probably the most important year
in the invention of AI.
Because in 1956, for the firs time,
the term artificial intelligence was coined.
Alright.
So the term artificial intelligence
was coined by John McCarthy
at the Dartmouth Conference in 1956.
Coming to the year 1959,
the first AI laboratory was established.
This period marked the research era for AI.
So the first AI lab where research was performed
is the MIT lab,
which is still running til date.
In 1960, the first robot was introduced
to the General Motors assembly line.
In 1961, the first chatbot was invented.
Now we have Siri, we have Alexa.
But in 1961,
there was a chatbot known as Eliza,
which was introduced.
This is followed by the famous IBM Deep Blue.
In 1997, the news broke down
that IBM's Deep Blue beats the world champion,
Garry Kasparov, in the game of chess.
So this was kind of the first accomplishment of AI.
It was able to beat the world champion at chess.
So in 2005, when the DARPA Grand Challenge was held,
a robotic car named Stanley,
which was built by Stanford's racing team,
won the DARPA Grand Challenge.
That was another big accomplish of AI.
In 2011, IBM's question answering system, Watson,
defeated the two greatest Jeopardy champions,
Brad Rutter and Ken Jennings.
So guys, this was how AI evolved.
It started off as a hypothetical situation.
Right now it's the most important technology
in today's world.
If you look around every where,
everything around us is run through AI deep learning
or machine learning.
So since the emergence of AI in the 1950s,
we have actually seen an exponential growth
and its potential.
So AI covers domains such as machine learning,
deep learning, neural networks,
natural language processing,
knowledge based, expert systems and so on.
It is also made its way into computer vision
and image processing.
Now the question here is if AI has been here
for over half a century,
why has it suddenly gain so much importance?
Why are we talking about artificial intelligence now?
Let me tell you the main reasons for the demand of AI.
The first reason is what we have
more computation power now.
So, artificial intelligence requires
a lot of computing power.
Recently, many advances have been made
and complex deep learning models are deployed.
And one of the greatest technology
that made this possible are GPUs.
Since we have more computational power now,
it is possible for us to implement AI
in our daily aspects.
Second most important reason is that
we have a lot of data at present.
We're generating data at an immeasurable pace.
We are generating data through social media,
through IoT devices.
Every possible way, there's a lot of data.
So we need to find a method or a solution
that can help us process this much data,
and help us derive useful insight,
so that we can grow business with the help of data.
Alright, so, that process
is basically artificial intelligence.
So, in order to have a useful AI agent
to make smart decisions
like telling which item to recommend
next when you shop online,
or how to classify an object from an image.
AI are trained on large data sets,
and big data enables us to do this more efficiently.
Next reason is now we have better algorithms.
Right now we have very effective algorithms
which are based on the idea of neural networks.
Neural networks is nothing but
the concept behind deep learning.
Since we have better algorithms
which can do better computations
and quicker computations with more accuracy,
the demand for AI has increased.
Another reason is that universities, governments,
startup, and tech giants are all investing in AI.
Okay, so companies like Google, Amazon,
Facebook, Microsoft,
all of these companies have heavily invested
in artificial intelligence
because they believe that AI is the future.
So AI is rapidly growing both as a field of study
and also as an economy.
So, actually, this is the right time
for you to understand what is AI and how it works.
So let's move on and understand
what exactly artificial intelligence is.
The term artificial intelligence
was first coined in the year 1956 by John McCarthy
at the Dartmouth Conference.
I already mentioned this before.
It was the birth of AI in the 1956.
Now, how did he define artificial intelligence?
John McCarthy defined AI as the science and engineering
of making intelligent machines.
In other words, artificial intelligence
is the theory and development of computer systems
able to perform task
that normally require human intelligence,
such as visual perception, speech recognition,
decision making, and translation between languages.
So guys, in a sense, AI is a technique of getting machines
to work and behave like humans.
In the rest past, artificial intelligence
has been able to accomplish this
by creating machines and robots
that have been used in wide range of fields,
including healthcare, robotics, marketing,
business analytics, and many more.
With this in mind,
let's discuss a couple of real world application of AI,
so that you understand how important artificial intelligence
is in today's world.
Now, one of the most famous applications
of artificial intelligence
is the Google predictive search engine.
When you begin typing a search term
and Google makes recommendations for you to choose from,
that is artificial intelligence in action.
So predictive searches are based on data
that Google collects about you,
such as your browser history, your location,
your age, and other personal details.
So by using artificial intelligence,
Google attempts to guess what you might be trying to find.
Now behind this,
there's a lot of natural language processing,
deep learning, and machine learning involved.
We'll be discussing all of those concepts
in the further slides.
It's not very simple to create a search engine,
but the logic behind Google search engine
is artificial intelligence.
Moving on, in the finance sector,
JP Morgan Chase's Contract Intelligence Platform
uses machine learning, artificial intelligence,
and image recognition software
to analyze legal documents.
Now let me tell you that manually reviewing
around 12,000 agreements took over 36,000 hours.
That's a lot of time.
But as soon as this task was replaced by AI machine,
it was able to do this in a matter of seconds.
So that's the difference between artificial intelligence
and manual or human work.
Even though AI cannot think and reason like humans,
but their computational power is very strong
compared to humans,
because the machine learning algorithm,
deep learning concepts, and natural language processing,
AI has reach a stage wherein it can compute
the most complex of complex problems
in a matter of seconds.
Coming to healthcare, IBM is one of the pioneers
that has developed AI software,
specifically for medicine.
Let me tell you that more than 230 healthcare organizations
use IBM AI technology,
which is basically IBM Watson.
In 2016, IBM Watson technology was able to cross reference
20 million oncology records quickly
and correctly diagnose a rare leukemia
condition in a patient.
So, it basically went through 20 million records,
which it probably did in a matter of second or minutes,
max to max.
And then it correctly diagnosed a patient
with a rare leukemia.
Knowing that machines are now used
in medical fields as well,
it shows how important AI has become.
It has reached every domains of our lives.
Let me give you another example.
The Google's AI Eye Doctor
is another initiative, which is taken by Google,
where they're working with an Indian eye care chain
to develop artificial intelligence system
which can examine retinal scans
and identify a condition called
diabetic retinopathy which can cause blindness.
Now in social media platforms like Facebook,
artificial intelligence is used for face verification
wherein you make use of machine learning
and deep learning concept
in order to detect facial features and tag your friends.
All the auto tagging feature that you see in Facebook,
behind that there's machine learning,
deep learning, neural networks.
There's only AI behind it.
So we're actually unaware
that we use AI very regularly in our life.
All the social media platforms
like Instagram, Facebook, Twitter,
they heavily rely on artificial intelligence.
Another such example is Twitter's AI
which is being used to identify any sort of hate speech
and terroristic languages in tweets.
So again, it makes use of machine leaning,
deep learning, natural language processing
in order to filter out any offensive
or any reportable content.
Now recently, the company discovered
around 300,000 terroristic link accounts
and 95% of these were found by non-human
artificially intelligent machines.
Coming to virtual assistants,
we have virtual assistants like Siri and Alexa right now.
Let me tell you about another newly released
Google's virtual assistant called the Google Duplex,
which has astonished millions of people around the world.
Not only can it respond to calls
and book appointments for you,
it also adds a human touch.
So it adds human filters and all of that.
It makes it sound very realistic.
It's actually very hard to distinguish between
human and the AI speaking over the phone.
Another famous application is AI is self-driving cars.
So, artificial intelligence implements computer vision,
image detection, deep learning,
in order to build cars
that can automatically detect any objects or any obstacles
and drive around without human intervention.
So these are fully automated self-driving cars.
Also, Elon Musk talks a lot about how AI is implemented
in Tesla's self-driving cars.
He quoted that Tesla will have fully self-driving cars
ready by the end of the year,
and robo taxi version that can ferry passengers
without anyone behind the wheel.
So if you look at it, AI is actually used
by the tech giants.
A lot of tech giant companies like Google, Tesla, Facebook,
all of these data-driven companies.
In fact, Netflix also makes use of AI,.
So, coming to Netflix.
So with the help of artificial intelligence
and machine learning,
Netflix has developed a personalized movie recommendation
for each of its users.
So if each of you opened up Netflix
and if you look at the type of movies
that are recommended to you, they are different.
This is because Netflix studies
each user's personal details,
and tries to understand what each user is interested in
and what sort of movie patterns each user has,
and then it recommends movies to them.
So Netflix uses the watching history of other users
with similar taste to recommend
what you may be most interested in watching next,
so that you can stay engaged
and continue your monthly subscription.
Also, there's a known fact that over 75% of what you watch
is recommended by Netflix.
So their recommendation engine is brilliant.
And the logic behind their recommendation engine
is machine learning and artificial intelligence.
Apart from Netflix, Gmail also uses AI on a everyday basis.
If you open up your inbox right now,
you will notice that there are separate sections.
For example, we have primary section,
social section, and all of that.
Gmail has a separate section called the spam mails also.
So, what Gmail does is it makes use of
concepts of artificial intelligence
and machine learning algorithms
to classify emails as spam and non-spam.
Many times certain words or phrases
are frequently used in spam emails.
If notice your spam emails,
they have words like lottery, earn, full refund.
All of this denotes that the email
is more likely to be a spam one.
So such words and correlations are understood
by using machine learning and natural language processing
and a few other aspects of artificial intelligence.
So, guys, these were the common applications
of artificial intelligence.
Now let's discuss the different types of AI.
So, AI is divided into three different evolutionary stages,
or you can say that there are three stages
of artificial intelligence.
Of course, we have artificial narrow intelligence
followed by artificial general intelligence,
and that is followed by artificial super intelligence.
Artificial narrow intelligence,
which is also known as weak AI,
it involves applying artificial intelligence
only to specific task.
So, many currently existing systems
that claim to use artificial intelligence
are actually operating as weak AI
focused on a narrowly defined specific problem
Let me give you an example
of artificial narrow intelligence.
Alexa is a very good example of weak AI.
It operates within unlimited pre-defined range of functions.
There's no genuine intelligence
or there is no self awareness,
despite being a sophisticated example of weak AI.
The Google search engine, Sophia the humanoid,
self-driving cars, and even the famous AlphaGo
fall under the category of weak AI.
So guys, right now we're at the stage
of artificial narrow intelligence or weak AI.
We actually haven't reached artificial general intelligence
or artificial super intelligence,
but let's look at what exactly it would be like
if we reach artificial general intelligence.
Now artificial general intelligence
which is also known as strong AI,
it involves machines that posses the ability
to perform any intelligent task that a human being can.
Now this is actually something
that a lot of people don't realize.
Machines don't posses human-like abilities.
They have a very strong processing unit
that can perform high-level computations,
but they're not yet capable of doing the simple
and the most reasonable things that a human being can.
If you tell a machine to process like a million documents,
it'll probably do that in a matter of 10 seconds,
or a minute, or even 10 minutes.
But if you ask a machine to walk up to your living room
and switch on the TV,
a machine will take forever to learn that,
because machines don't have the reasonable way of thinking.
They have a very strong processing unit,
but they're not yet capable
of thinking and reasoning like a human being.
So that's exactly why we're still stuck
on artificial narrow intelligence.
So far we haven't developed any machine
that can fully be called strong AI,
even though there are examples of AlphaGo Zero
which defeated AlphaGo in the game of Go.
AlphaGo Zero basically learned in a span of four months.
It learned on its own without any human intervention.
But even then, it was not classified
as a fully strong artificial intelligence,
because it cannot reason like a human being.
Moving onto artificial super intelligence.
Now this is a term referring to the time
when the capabilities of a computer
will surpass that of a human being.
In all actuality, I'll take a while for us
to achieve artificial super intelligence.
Presently, it's seen as a hypothetical situation
as depicted in movies and any science fiction books
wherein machines have taken over the world,
movies like Terminator and all of that
depict artificial super intelligence.
These don't exist yet,
which we should be thankful for,
but there are a lot of people
who speculate that artificial super intelligence
will take over the world by the year 2040.
So guys, these were the different types
or different stages of artificial intelligence.
To summarize everything, like I said before,
narrow intelligence is the only thing that exist for now.
We have only weak AI or weak artificial intelligence.
All the major AI technologies that you see
are artificial narrow intelligence.
We don't have any machines which are capable of thinking
like human beings or reasoning like a human being.
Now let's move on and discuss
the different programming language for AI.
So there are actually N number of language
that can be used for artificial intelligence.
I'm gonna mention a few of them.
So, first, we have Python.
Python is probably the most famous language
for artificial intelligence.
It's also known as the most effective language for AI,
because a lot of developers prefer to use Python.
And a lot of scientists are also comfortable
with the Python language.
This is partly because the syntaxes
which belong to Python are very simple
and they can be learned very easily.
It's considered to be one of the most
easiest language to learn.
And also many other AI algorithms
and machine learning algorithms
can be easily implemented in Python,
because there are a lot of libraries
which are predefined functions for these algorithms.
So all you have to do is you have to call that function.
You don't actually have to call your algorithm.
So, Python is considered the best choice
for artificial intelligence.
With Python stands R,
which is a statistical programming language.
Now R is one of the most effective language
and environment for analyzing and manipulating the data
for statistical purpose.
It is a statistical programming language.
So using R we can easily produce
well designed publication quality plots,
including mathematical symbol and formula, wherever needed.
If you ask me, I think R is also one of the
easiest programming language to learn.
The syntax is very similar to English language,
and it also has N number of libraries
that support statistics, data science,
AI, machine learning, and so on.
It also has predefined functions
for machine learning algorithms,
natural language processing, and so on.
So R is also a very good choice
if you want to get started with programming languages
for machine learning or AI.
Apart from this, we have Java.
Now Java can also be considered as a good choice
for AI development.
Artificial intelligence has a lot to do
with search algorithms,
artificial neural networks, and genetic programming,
and Java provides many benefits.
It's easy to use.
Debugging is very easy, package services.
There is simplified work with large scale projects.
There's a good user interaction,
and graphical representation of data.
It has something known as the standard widget toolkit,
which can be used for making graphs and interfaces.
So, graphic virtualization is actually
a very important part of AI,
or data science, or machine learning for that matter.
Let me list out a few more languages.
We also have something known as Lisp.
Now shockingly, a lot of people have not heard
of this language.
This is actually the oldest and the most suited language
for the development of artificial intelligence.
It is considered to be a language
which is very suited for the development
of artificial intelligence.
Now let me tell you that this language
was invented by John McCarthy
who's also known as the father of artificial intelligence.
He was the person who coined the term
artificial intelligence.
It has the capability of processing symbolic information.
It has excellent prototyping capabilities.
It is easy,
and it creates dynamic objects with a lot of ease.
There's automatic garbage collection in all of that.
But over the years, because of advancements,
many of these features
have migrated into many other languages.
And that's why a lot of people don't go for Lisp.
There are a lot of new languages
which have more effective features
or which have better packages you can see.
Another language I like to talk about is Prolog.
Prolog is frequently used in knowledge base
and expert systems.
The features provided by Prolog
include pattern matching, freebase data structuring,
automatic back tracking and so on.
All of these features provide
a very powerful and flexible programming framework.
Prolog is actually widely used in medical projects
and also for designing expert AI systems.
Apart from this, we also have C++,
we have SaaS, we have JavaScript
which can also be used for AI.
We have MATLAB, we have Julia.
All of these languages are actually considered
pretty good languages for artificial intelligence.
But for now, if you ask me
which programming language should I go for,
I would say Python.
Python has all the possible packages,
and it is very easy to understand and easy to learn.
So let's look at a couple of features of Python.
We can see why we should go for Python.
First of all, Python was created
in the year 1989.
It is actually a very easy programming language.
That's one of the reasons why
a lot of people prefer Python.
It's very easy to understand.
It's very easy to grasp this language.
So Python is an interpreted, object-oriented,
high-level programming language,
and it can be very easily implemented.
Now let me tell you a few features of Python.
It's very simple and easy to learn.
Like I mentioned,
it is one of the easiest programming language,
and it also free and open source.
Apart from that, it is a high-level language.
You don't have to worry about
anything like memory allocation.
It is portable,
meaning that you can use it on any platform
like Linux, Windows, Macintosh, Solaris, and so on.
It support different programming paradigms
like object-oriented and procedure oriented programming,
and it is extensible,
meaning that it can invoke C and C++ libraries.
Apart from this, let me tell you that Python
is actually gaining unbelievable huge momentum in AI.
The language is used to develop data science algorithms,
machine learning algorithms, and IoT projects.
The other advantages to Python also,
the fact that you don't have to code much
when it comes to Python for AI or machine learning.
This is because there are ready-made packages.
There are predefined packages
that have all the function and algorithm stored.
For example, there is something known as PiBrain,
which can be used for machine learning,
NumPy which can be used for scientific computation,
Pandas and so on.
There are N number of libraries in Python.
So guys, I'm now going to go into depth of Python.
I'm now going to explain Python to you,
since this session is about artificial intelligence.
So, those of you who don't know much about Python
or who are new to Python,
I will leave a couple of links in the description box.
You all can get started with programming
and any other concepts or any other doubts
that you have on Python.
We have a lot of content around programming with Python
or Python for machine learning and so on.
Now let's move on and talk about
one of the most important aspects
of artificial intelligence,
which is machine learning.
Now a lot of people always ask me this question.
Is machine learning and artificial intelligence
the same thing?
Well, both of them are not the same thing.
The difference between AI and machine learning
is that machine learning is used in artificial intelligence.
Machine learning is a method
through which you can feed a lot of data to a machine
and make it learn.
Now AI is a vast of field.
Under AI, we have machine learning, we have NLP,
we have expert systems, we have image recognition,
object detection, and so on.
We have deep learning also.
So, AI is sort of a process or it's a methodology
in which you make machines
mimic the behavior of human beings.
Machine learning is a way
in which you feed a lot of data to a machine,
so that it can make it's own decisions.
Let's get into depth about machine learning.
So first, we'll understand the need for machine learning
or why machine learning came into existence.
Now the need for machine learning
begins since the technical revolution itself.
So, guys, since technology became the center of everything,
we've been generating an immeasurable amount of data.
As per research, we generate around
2.5 quintillion bytes of data every single data
every single day.
And it is estimated that by this year, 2020,
1.7 mb of data will be created every second
for every person on earth.
So as I'm speaking to you right now,
I'm generating a lot of data.
Now your watching this video on YouTube
also accounts for data generation.
So there's data everywhere.
So with the availability of so much data,
it is finally possible to build predictive models
that can study and analyze complex data
to find useful insights and deliver more accurate results.
So, top tier companies like Netflix and Amazon
build such machine learning models
by using tons of data
in order to identify any profitable opportunity
and avoid any unwanted risk.
So guys, one thing you all need to know is that
the most important thing for artificial intelligence
is data.
For artificial intelligence
or whether it's machine learning or deep learning,
it's always data.
And now that we have a lot of data,
we can find a way to analyze, process,
and draw useful insights from this data
in order to help us grow businesses
or to find solutions to some problems.
Data is the solution.
We just need to know how to handle the data.
And the way to handle data
is through machine learning, deep learning,
and artificial intelligence.
A few reasons why machine learning is so important
is, number one, due to increase in data generation.
So due to excessive production of data,
we need to find a method that can be used
to structure, analyze, and draw useful insights from data,
this is where machine learning comes in.
It is used to solve problems and find solutions
through the most complex task faced by organizations.
Apart form this, we also needed to improve decision making.
So by making use of various algorithms,
machine learning can be used to make
better business decisions.
For example, machine learning is used to focus sales.
It is used to predict any downfalls n the stock market
or identify any sort of risk and anomalies.
Other reasons include that machine learning helps us
uncover patterns and trends in data.
So finding hidden patterns
and extracting key insights fro data
is the most important part of machine learning.
So by building predictive models
and using statistical techniques,
machine learning allows you to dig beneath the surface
and explode the data at a minute scale.
Understanding data and extracting patterns manually
takes a lot of time.
It'll take several days for us
to extract any useful information from data.
But if you use machine learning algorithms,
you can perform similar computations in less than a second.
Another reason is we need to solve complex problems.
So from detecting the genes
linked to the deadly ALS disease,
to building self-driving cars,
machine learning can be used
to solve the most complex problems.
At present, we also found a way to spot stars
which are 2,400 light years away from our planet.
Okay, all of this is possible through AI,
machine learning, deep learning, and these techniques.
So to sum it up,
machine learning is very important at present
because we're facing a lot of issues with data.
We're generating a lot of data,
and we have to handle this data
in such a way that in benefits us.
So that's why machine learning comes in.
Moving on, what exactly is machine learning?
So let me give you a short history of machine learning.
So machine learning was first coined by Arthur Samuel
in the year 1959,
which is just three years from
when artificial intelligence was coined.
So, looking back, that year was probably
the most significant in terms of technological advancement,
because most of the technologies today
are based on the concept of machine learning.
Most of the AI technologies itself
are based on the concept of
machine learning and deep learning.
Don't get confused about
machine learning and deep learning.
We'll discuss about deep learning in the further slides,
where we'll also see the difference
between AI, machine learning, and deep learning.
So coming back to what exactly machine learning is,
if we browse through the internet,
you'll find a lot of definitions about
what exactly machine learning is.
One of the definitions I found was
a computer program is said to learn from experience E
with respect to some class of task T
and performance measure P if its performance at task in T,
as measured by P, improves with experience E.
That's very confusing, so let me just narrow it down to you.
In simple terms, machine learning is a subset
of artificial intelligence
which provides machines the ability
to learn automatically and improve with experience
without being explicitly programmed to do so.
In the sense, it is the practice
of getting machines to solve problems
by gaining the ability to think.
But now you might be thinking
how can a machine think or make decisions.
Now machines are very similar to humans.
Okay, if you feed a machine a good amount of data,
it will learn how to interpret, process,
and analyze this data by using machine learning algorithms,
and it will help you solve world problems.
So what happens here is a lot of data
is fed to the machine.
The machine will train on this data
and it'll build a predictive model
with the help of machine learning algorithms
in order to predict some outcome
or in order to find some solution to a problem.
So it involves data.
You're gonna train the machine
and build a model by using machine learning algorithms
in order to predict some outcome
or to find a solution to a problem.
So that is a simple way of understanding
what exactly machine learning is.
I'll be going into more depth about machine learning,
so don't worry if you have understood anything as of now.
Now let's discuss a couple terms
which are frequently used in machine learning.
So, the first definition that we come across very often
is an algorithm.
So, basically, a machine learning algorithm
is a set of rules and statistical techniques
that is used to learn patterns from data
and draw significant information from it.
Okay.
So, guys, the logic behind a machine learning model
is basically the machine learning algorithm.
Okay, an example of a machine learning algorithm
is linear regression, or decision tree, or a random forest.
All of these are machine learning algorithms.
We'll define the logic behind
a machine learning model.
Now what is a machine learning model?
A model is actually the main component
of a machine learning process.
Okay, so a model is trained by using
the machine learning algorithm.
The difference between an algorithm and a model is that
an algorithm maps all the decisions
that a model is supposed to take
based on the given input
in order to get the correct output.
So the model will use
the machine learning algorithm
in order to draw useful insights from the input
and give you an outcome that is very precise.
That's the machine learning model.
The next definition we have is predictor variable.
Now a predictor variable is any feature of the data
that can be used to predict the output.
Okay, let me give you an example
to make you understand what a predictor variable is.
Let's say you're trying to predict the height of a person,
depending on his weight.
So here your predictor variable becomes your weight,
because you're using the weight of a person
to predict the person's height.
So your predictor variable becomes your weight.
The next definition is response variable.
Now in the same example,
height would be the response variable.
Response variable is also known as
the target variable or the output variable.
This is the variable that you're trying to predict
by using the predictor variables.
So a response variable is the feature
or the output variable that needs to be predicted
by using the predictor variables.
Next, we have something known as training data.
Now training and testing data are terminologies
that you'll come across very often
in a machine learning process.
So training data is basically the data that I used
to create the machine learning model.
So, basically in a machine learning process,
when you feed data into the machine,
it'll be divided into two parts.
So splitting the data into two parts
is also known as data splicing.
So you'll take your input data,
you'll divide it into two sections.
One you'll call the training data,
and the other you'll call the testing data.
So then you have something known as the testing data.
The training data is basically used
to create the machine learning model.
The training data helps the model to identify
key trends and patterns
which are essential to predict the output.
Now the testing data is, after the model is trained,
it must be tested in order to evaluate how accurately
it can predict an outcome.
Now this is done by using the testing data.
So, basically, the training data is used to train the model.
The testing data is used to test
the efficiency of the model.
Now let's move on and get our next topic,
which is machine learning process.
So what is the machine learning process?
Now the machine learning process
involves building a predictive model
that can be used to find a solution
for a problem statement.
Now in order to solve any problem in machine learning,
there are a couple of steps that you need to follow.
Let's look at the steps.
The first step is you define the objective of your problem.
And the second step is data gathering,
which is followed by preparing your data,
data exploration, building a model,
model evaluation, and finally making predictions.
Now, in order to understand the machine learning process,
let's assume that you've been given a problem
that needs to be solved by using machine learning.
So the problem that you need to solve is
we need to predict the occurrence of rain
in your local area by using machine learning.
So, basically, you need to predict
the possibility of rain by studying the weather conditions.
So what we did here is we
basically looked at step number one,
which is define the objective of the problem.
Now here you need to answer questions such as
what are we trying to predict.
Is that output going to be a continuous variable,
or is it going to be a discreet variable?
These are the kinds of questions that you need to answer
in the first page,
which is defining the objective of the problem, right?
So yeah, exactly what are the target feature.
So here you need to understand
which is your target variable
and what are the different predictor variables
that you need in order to predict this outcome.
So here our target variable will be basically
a variable that can tell us
whether it's going to rain or not.
Input data is we'll need data such as maybe
the temperature on a particular day
or the humidity level, the precipitation, and so on.
So you need to define the objective at this stage.
So basically, you have to form an idea of the problem
at this storage.
Another question that you need to ask yourself
is what kind of problem are you solving.
Is this a binary classification problem,
or is this a clustering problem,
or is this a regression problem?
Now, a lo of you might not be familiar
with the terms classification clustering
and regression in terms of machine learning.
Don't worry, I'll explain all of these terms
in the upcoming slides.
All you need to understand at step one
is you need to define how you're going to solve the problem.
You need to understand what sort of data
you need to solve the problem,
how you're going to approach the problem,
what are you trying to predict,
what variables you'll need in order to predict the outcome,
and so on.
Let's move on and look at step number two,
which is data gather.
Now in this stage, you must be asking questions such as,
what kind of data is needed to solve this problem?
And is this data available?
And if it is available, from where can I get this data
and how can I get the data?
Data gathering is one of the most time-consuming
steps in machine learning process.
If you have to go manually and collect the data,
it's going to take a lot of time.
But lucky for us, there are a lot of resources online,
which were wide data sets.
All you need to do is web scraping
where you just have to go ahead and download data.
One of the websites I can tell you all about is Cargill.
So if you're a beginner in machine learning,
don't worry about data gathering and all of that.
All you have to do is go to websites such as cargill
and just download the data set.
So coming back to the problem that we are discussing,
which is predicting the weather,
the data needed for weather forecasting
includes measures like humidity level,
the temperature, the pressure, the locality,
whether or not you live in a hill station,
such data has to be collected or stored for analysis.
So all the data is collected
during the data gathering stage.
This step is followed by data preparation,
or also known as data cleaning.
So if you're going around collecting data,
it's almost never in the right format.
And eve if you are taking data
from online resources from any website,
even then, the data will require cleaning and preparation.
The data is never in the right format.
You have to do some sort of preparation
and some sort of cleaning
in order to make the data ready for analysis.
So what you'll encounter while cleaning data
is you'll encounter a lot of inconsistencies
in the data set,
like you'll encounter som missing values,
redundant variables, duplicate values, and all of that.
So removing such inconsistencies is very important,
because they might lead to any wrongful
computations and predictions.
Okay, so at this stage you can scan the data set
for any inconsistencies,
and you can fix them then and there.
Now let me give you a small fact about data cleaning.
So there was a survey that was ran last year or so.
I'm not sure.
And a lot of data scientists were asked
which step was the most difficult or the most
annoying and time-consuming of all.
And 80% of the data scientist said
it was data cleaning.
Data cleaning takes up 80% of their time.
So it's not very easy to get rid of missing values
and corrupted data.
And even if you get rid of missing values,
sometimes your data set might get affected.
It might get biased because maybe one variable
has too many missing values,
and this will affect your outcome.
So you'll have to fix such issue,
we'll have to deal with all of this missing data
and corrupted data.
So data cleaning is actually one of the hardest steps
in machine learning process.
Okay, now let's move on and look at our next step,
which is exploratory data analysis.
So here what you do is basically become
a detective in the stage.
So this stage, which is EDA or exploratory data analysis,
is like the brainstorming stage of machine learning.
Data exploration involves understanding the patterns
and the trends in your data.
So at this stage, all the useful insights are drawn
and any correlations between the various variables
are understood.
What do I mean by trends and patterns and correlations?
Now let's consider our example
which is we have to predict the rainfall
on a particular day.
So we know that there is a strong possibility of rain
if the temperature has fallen law.
So we know that our output will depend on
variables such as temperature, humidity, and so on.
Now to what level it depends on these variables,
we'll have to find out that.
We'll have to find out the patterns,
and we'll find out the correlations
between such variables.
So such patterns and trends have to be understood
and mapped at this stage.
So this is what exploratory data analysis is about.
It's the most important part of machine learning.
This is where you'll understand
what exactly your data is
and how you can form the solution to your problem.
The next step in a machine learning process
is building a machine learning module.
So all the insights and the patterns
that you derive during the data exploration
are used to build a machine learning model.
So this stage always begins by splitting the data set
into two parts, which is training data and testing data.
I've already discussed with you
that the data that you used in a machine learning process
is always split into two parts.
We have the training data and we have the testing data.
Now when you're building a model,
you always use the training data.
So you always make use of the training data
in order to build the model.
Now a lot of you might be asking what is training data.
Is it different from the input data
that you're feeding with the machine
or is it different from the testing data?
Now training data is the same input data
that you're feeding to the machine.
The only difference is that you're
splitting the data set into two.
You're randomly picking 80% of your data
and you're assigning for training purpose.
And the rest 20%, probably,
you'll assign it for testing purpose.
So guys, always remember another thing that
the training data is always much more
than your testing data,
obviously because you need to train your machine.
And the more data you feed the machine
during the training phase,
the better it will be during the testing phase.
Obviously, it'll predict better outcomes
if it is being trained on more data.
Correct?
So the model is basically using
the machine learning algorithm that predicts the output
by using the data fed to it.
Now in the case of predicting rainfall,
the output will be a categorical variable,
because we'll be predicting
whether it's going to rain or not.
Okay, so let's say we have an output variable called rain.
The two possible values that this variable can take
is yes it's going to rain and no it won't rain.
Correct, so that is out come.
Our outcome is a classification or a categorical variable.
So for such cases where your outcome
is a categorical variable,
you'll be using classification algorithms.
Again, example of a classification algorithm
is logistic regression
or you can also support vector machines,
you can use K nearest neighbor,
and you can also use naive Bayes, and so on.
Now don't worry about these terms,
I'll be discussing all these algorithms with you.
But just remember that while you're building
a machine learning model,
you'll make use of the training data.
You'll train the model by using the training data
and the machine learning algorithm.
Now like I said, choosing the machine learning algorithm,
depends on the problem statement
that you're trying to solve
because of N number of machine learning algorithms.
We'll have to choose the algorithm
that is the most suitable for your problem statement.
So step number six is model evaluation
and optimization.
Now after you've done building a model
by using the training data set,
it is finally time to put the model road test.
The testing data set is used to check
the efficiency of the model
and how accurately it can predict the outcome.
So once the accuracy is calculated,
any further improvements in the model
can be implemented during this stage.
The various methods that can help you
improve the performance of the model,
like you can use parameter tuning
and cross validation methods
in order to improve the performance of the model.
Now the main things you need to remember
during model evaluation and optimization
is that model evaluation is nothing but
you're testing how well your model can predict the outcome.
So at this stage, you will be using the testing data set.
In the previous stage, which is building a model,
you'll be using the training data set.
But in the model evaluation stage,
you'll be using the testing data set.
Now once you've tested your model,
you need to calculate the accuracy.
You need to calculate how accurately
your model is predicting the outcome.
After that, if you find that you need to
improve your model in some way or the other,
because the accuracy is not very good,
then you'll use methods such as parameter tuning.
Don't worry about these terms,
I'll discuss all of this with you,
but I'm just trying to make sure
that you're understanding the concept
behind each of the phases and machine learning.
It's very important you understand each step.
Okay, now let's move on and look at
the last stage of machine learning, which is predictions.
Now, once a model is evaluated
and once you've improved it,
it is finally used to make predictions.
The final output can either be a categorical variable
or a continuous variable.
Now all of this depends on your problem statement.
Don't get confused about continuous variables,
categorical variables.
I'll be discussing all of this.
Now in our case, because we're predicting
the occurrence of rainfall,
the output will be categorical variable.
It's obvious because we're predicting
whether it's going to rain or not.
The result, we understand
that this is a classification problem
because we have a categorical variable.
So that was the entire machine learning process.
Now it's time to learn about the different ways
in which machines can learn.
So let's move ahead
and look at the types of machine learning.
Now this is one of the most
interesting concepts in machine learning,
the three different ways in which machines learn.
There is something known as supervised learning,
unsupervised learning, and reinforcement learning.
So we'll go through this one by one.
We'll understand what supervised learning is first,
and then we'll look at the other two types.
So defined supervised learning,
it is basically a technique in which we teach
or train the machine by using the data,
which is well labeled.
Now, in order to understand supervised learning,
let's consider a small example.
So, as kids, we all needed guidance to solve math problems.
A lot of us had trouble solving math problems.
So our teachers always help us understand what addition is
an dhow it is done.
Similarly, you can think of supervised learning
as a type of machine learning
that involves a guide.
The label data set is a teacher
that will train you to understand the patterns in the data.
So the label data set is nothing but the training data set.
I'll explain more about this in a while.
So, to understand supervised learning better,
let's look at the figure on the screen.
Right here we're feeding the machine
image of Tom and Jerry,
and the goal is for the machine to identify
and classify the images into two classes.
One will contain images of Tom
and the the other will contain images of Jerry.
Now the main thing that you need to note
in supervised learning is a training data set.
The training data set is going to be very well labeled.
Now what do I mean when I say that
training data set is labeled.
Basically, what we're doing is we're telling the machine
this how Tom looks and this is how Jerry looks.
By doing this, you're training the machine
by using label data.
So the main thing that you're doing is you're labeling
every input data that you're feeding to the model.
So, basically, you're entire training data set is labeled.
Whenever you're giving an image of Tom,
there's gonna be a label there saying this is Tom.
And when you're giving an image of Jerry,
you're saying that this is how Jerry looks.
So, basically, you're guiding the machine
and you're telling that, "Listen, this is how Tom looks,
"this is how Jerry looks,
"and now you need to classify them
"into two different classes."
That's how supervised learning works.
Apart from that, it's the same old process.
After getting the input data,
you're gonna perform data cleaning.
Then there's exploratory data analysis,
followed by creating the model
by using the machine learning algorithm,
and then this is followed by model evaluation,
and finally, your predictions.
Now, one more thing to note here is that
the output that you get by using supervised learning
is also labeled output.
So, basically, you'll get two different classes
of name Tom and one of name Jerry,
and you'll get them labeled.
That is how supervised learning works.
The most important thing in supervised learning
is that you're training the model by using
labeled data set.
Now let's move on and look at unsupervised learning.
We look at the same example and understand
how unsupervised learning works.
So what exactly is unsupervised learning?
Now this involves training by using unlabeled data
and allowing the model to act on that information
without any guidance.
Alright.
Like the name suggest itself,
there is no supervision here.
It's unsupervised learning.
So think of unsupervised learning as a smart kid
that learns without any guidance.
Okay, in this type of machine learning,
the model is not fed with any label data,
as in the model has no clue that this is
the image of Tom and this is Jerry.
It figures out patterns
and the difference between Tom and Jerry on its own
by taking in tons and tons of data.
Now how do you think the machine identifies this as Tom,
and then finally gives us the output like
yes this is Tom, this is Jerry.
For example, it identifies prominent features of Tom,
such as pointy ears, bigger in size, and so on,
to understand that this image is of type one.
Similarly, it finds out features in Jerry,
and knows that this image is of type two,
meaning that the first image
is different from the second image.
So what the unsupervised learning algorithm
or the model does is it'll form two different clusters.
It'll form one cluster which are very similar,
and the other cluster which is very different
from the first cluster.
That's how unsupervised learning works.
So the important things that you need to know
in unsupervised learning
is that you're gonna feed the machine unlabeled data.
The machine has to understand the patterns
and discover the output on its own.
And finally, the machine will form clusters
based on feature similarity.
Now let's move on and locate
the last type of machine learning,
which is reinforcement learning.
Reinforcement learning is quite different
when compared to supervised and unsupervised learning.
What exactly is reinforcement learning?
It is a part of machine learning where an agent
is put in an environment,
and he learns to behave in this environment
by performing certain actions,
and observing the rewards which is gets from those actions.
To understand what reinforcement learning is,
imagine that you were dropped off at an isolate island.
What would you do?
Now panic.
Yes, of course, initially, we'll all panic.
But as time passes by, you will learn
how to live on the island.
You will explode the environment,
you will understand the climate conditions,
the type of food that grows there,
the dangers of the island so on.
This is exactly how reinforcement learning works.
It basically involves an agent,
which is you stuck on the island,
that is put in an unknown environment, which is the island,
where he must learn by observing and performing
actions that result in rewards.
So reinforcement learning is mainly used
in advanced machine learning areas
such as self-driving cars and AlphaGo.
I'm sure a lot of you have heard of AlphaGo.
So, the logic behind AlphaGo
is nothing but reinforcement learning and deep learning.
And in reinforcement learning,
there is not really any input data given to the agent.
All he has to do is he has to explore
everything from scratch
it's like a newborn baby with no information about anything.
He has to go around exploring the environment,
and getting rewards, and performing some actions
which results in either rewards
or in some sort of punishment.
Okay.
So that sums up the types of machine learning.
Before we move ahead,
I'd like to discuss the difference
between the three types of machine learning,
just to make the concept clear to you all.
So let's start by looking at the definitions of each.
In supervised learning,
the machine will learn by using the label data.
In unsupervised learning, they'll be unlabeled data,
and the machine has to learn without any supervision.
In reinforcement learning, there'll be an agent
which interacts with the environment
by producing actions and discover errors or rewards
based on his actions.
Now what are the type of problems
that can be solved by using supervised, unsupervised,
and reinforcement learning.
When it comes to supervised learning,
the two main types of problems that are solved
is regression problems and classification problems.
When it comes to unsupervised learning,
it is association and clustering problems.
When it comes to reinforcement learning,
it's reward-based problems.
I'll be discussing regression, classification,
clustering, and all of this in the upcoming slides,
so don't worry if you don't understand this.
Now the type of data which is used in supervised learning
is labeled data.
In unsupervised learning, it unlabeled.
And in reinforcement learning,
we have no predefined data set.
The agent has to do everything from scratch.
Now the type of training involved
in each of these learnings.
In supervised learning, there is external supervision,
as in there is the labeled data set
which acts as a guide for the machine to learn.
In unsupervised learning, there's no supervision.
Again, in reinforcement learning,
there's no supervision at all.
Now what is the approach to solve problems
by using supervised, unsupervised,
and reinforcement learning?
In supervised learning, it is simple.
You have to mal the labeled input to the known output.
The machine knows what the output looks like.
So you're just labeling the input to the output.
In unsupervised learning,
you're going to understand the patterns
and discover the output.
Here you have no clue about what the input is.
It's not labeled.
You just have to understand the patterns
and you'll have to form clusters and discover the output.
In reinforcement learning, there is no clue at all.
You'll have to follow the trial and error method.
You'll have to go around your environment.
You'll have to explore the environment,
and you'll have to try some actions.
And only once you perform those actions,
you'll know that whether this is a reward-based action
or whether this is a punishment-based action.
So, reinforcement learning is totally based
on the concept of trial and error.
Okay.
A popular algorithm on the supervised learning include
linear regression, logistic regressions,
support vector machines K nearest neighbor,
naive Bayes, and so on.
Under unsupervised learning,
we have the famous K-means clustering method, C-means
and all of that.
Under reinforcement learning,
we have the famous learning Q-learning algorithm.
I'll be discussing these algorithms in the upcoming slides.
So let's move on and look at the next topic,
which is the types of problems solved
using machine learning.
Now this is what we were talking about earlier
when I said regression, classification,
and clustering problems.
Okay, so let's discuss what exactly I mean by that.
In machine learning, all the problems can be
classified into three types.
Every problem that is approached in machine learning
can be put interest one of these three categories.
Okay, so the first type is known as a regression,
then we have classification and clustering.
So, first, let's look at regression type of problems.
So in this type problem,
the output is always a continuous quantity.
For example, if you want to predict
the speed of a car, given the distance,
it is a regression problem.
Now a lot of you might not be very aware
of what exactly a continuous quantity is.
A continuous quantity is any quantity that can have
an infinite range of values.
For example, The weight of a person,
it is a continuous quantity,
because our weight can be 50, 50.1,
50.001,
5.0021,
50.0321 and so on.
It can have an infinite range of values, correct?
So the type of problem that you have to predict
a continuous quantity to make use of regression algorithms.
So, regression problems can be solved
by using supervised learning algorithms
like linear regression.
Next, we have classification.
Now in this type of problem,
the output is always a categorical value.
Now when I say categorical value,
it can be value such as
the gender of a person is a categorical value.
Now classifying emails into two two classes
like spam and non-spam is a classification problem
that can be solved by using
supervised learning classification algorithms,
like support vector machines, naive Bayes,
logistic regression, K nearest neighbor, and so on.
So, again, the main aim in classification
is to compute the category of the data.
Coming to clustering problems.
This type of problem involves
assigned input into two or more clusters
based on feature similarity.
Thus when I read this sentence,
you should understand that this is unsupervised learning,
because you don't have enough data about your input,
and the only option that you have is to form clusters
Categories are formed only when you know that
your data is of two type.
Your input data is labeled and it's of two types,
so it's gonna be a classification problem.
But when a clustering problem happens,
when you don't have much information about your input,
all you have to do is you have to find patterns
and you have to understand that
data points which are similar
are clustered into one group,
and data points which are different from the first group
are clustered into another group.
That's what clustering is.
An example is in Netflix what happens is
Netflix clusters their users into similar groups
based on their interest, based on their age,
geography, and so on.
This can be done by using unsupervised learning algorithms
like K-means.
Okay.
So guys, there were the three categories of problems
that can be solved by using machine learning.
So, basically, what I'm trying to say
is all the problems will fall into one of these categories.
So any problem that you give to a machine learning model,
it'll fall into one of these categories.
Okay.
Now to make things a little more interesting,
I have collected real world data sets
from online resources.
And what we're gonna do is we're going to try and understand
if this is a regression problem,
or a clustering problem, or a classification problem.
Okay.
Now the problem statement in here
is to study the house sales data set,
and build a machine learning model
that predicts the house pricing index.
Now the most important thing you need to understand
when you read a problem statement
is you need to understand what is your target variable,
what are the possible predictor variable that you'll need.
The first thing you should look at is your targe variable.
If you want to understand if this a classification,
regression, or clustering problem,
look at your target variable or your output variable
that you're supposed to predict.
Here you're supposed to predict the house pricing index.
Our house pricing index is obviously
a continuous quantity.
So as soon as you understand that,
you'll know that this is a regression problem.
So for this, you can make use of
the linear regression algorithm,
and you can predict the house pricing index.
Linear regression is the regression algorithm.
It is a supervised learning algorithm.
We'll discuss more about it in the further slides.
Let's look at our next problem statement.
Here you have to study a bank credit data set,
and make a decision about whether
to approve the loan of an applicant
based on his profile.
Now what is your output variable over here?
Your output variable is to predict whether you can
approve the loan of a applicant or not.
So, obviously, your output is going to be categorical.
It's either going to be yes or no.
Yes is basically approved loan.
No is reject loan.
So here, you understand that
this is a classification problem.
Okay.
So you can make use of algorithms like KNN algorithm
or you can make use of support vector machines
in order to do this.
So, support vector machine and KNN
which is K nearest neighbor algorithms
are basically supervised learning algorithm.
We'll talk more about that in the upcoming slides.
Moving on to our next problem statement.
Here the problem statement is to cluster
a set of movies as either good or average
based on the social media outreach.
Now if you look properly,
your clue is in the question itself.
The first line it says is to cluster a set of movies
as either good or average.
Now guys, whenever you have a problem statement
that is asking you to group the data set
into different groups
or to form different, different clusters,
it's obviously a clustering problem.
Right here you can make use
of the K-means clustering algorithm,
and you can form two clusters.
One will contain the popular movies
and the other will contain the non-popular movies.
These alright small examples of how you can use
machine learning to solve clustering problem,
the regression, and classification problems.
The key is you need to identify the type of problem first.
Now let's move on and discuss the different types
of machine learning algorithms.
So we're gonna start by discussing the different
supervised learning algorithms.
So to give you a quick overview,
we'll be discussing the linear regression,
logistic regression, and decision tree,
random forest, naive Bayes classifier,
support vector machines, and K nearest neighbor.
We'll be discussing these seven algorithms.
So without any further delay,
let's look at linear regression first.
Now what exactly is a linear regression algorithm?
So guys, linear regression is basically
a supervised learning algorithm
that is used to predict a continuous dependent variable y
based on the values of independent variable x.
Okay.
The important thing to note here
is that the dependent variable y,
the variable that you're trying to predict,
is always going to be a continuous variable.
But the independent variable x,
which is basically the predictor variables,
these are the variables that you'll be using
to predict your output variable,
which is nothing but your dependent variable.
So your independent variables or your predictive variables
can either be continuous or discreet.
Okay, there is not such a restriction over here.
Okay, they can be either continuous variables
or they can be discreet variables.
Now, again, I'll tell you what a continuous variable is,
in case you've forgotten.
It is a vary that has infinite number of possibilities.
So I'll give you an example of a person's weight.
It can be 160 pounds, or they can weigh 160.11 pounds,
or 160.1134 pounds and so on.
So the number of possibilities for weight is limitless,
and this is exactly what a continuous variable is.
Now in order to understand linear regression,
let's assume that you want to predict the
price of a stock over a period of time.
Okay.
For such a problem, you can make use of linear regression
by starting the relationship
between the dependent variable,
which is the stock price,
and the independent variable, which is the time.
You're trying to predict the stock price
over a period of time.
So basically, you're gonna check how the price of a stock
varies over a period of time.
So your stock price is going to be
your dependent variable or your output variable,
and the time is going to be your predictor variable
or your independent variable.
Let's not confuse it anymore.
Your dependent variable is your output variable.
Okay, your independent variable is your input variable
or your predictor variable.
So in our case, the stock price is obviously
a continuous quantity,
because the stock price can have
an infinite number of values.
Now the first step in linear regression
is always to draw out a relationship
between your dependent and your independent variable
by using the best fitting linear length.
We make an assumption that your dependent
and independent variable
is linearly related to each other.
We call it linear regression because
both the variables vary linearly,
which means that by plotting the relationship
between these two variables,
we'll get more of a straight line, instead of a curve.
Let's discuss the math behind linear regression.
So, this equation over here,
it denotes the relationship between your
independent variable x, which is here,
and your dependent variable y.
This is the variable you're trying to predict.
Hopefully, we all know that the equation
for a linear line in math is y equals mx plus c.
I hope all of you remember math.
So the equation for a linear line in math
is y equals to mx plus c.
Similarly, the linear regression equation
is represented along the same line.
Okay, y equals to mx plus c.
There's just a little bit of changes,
which I'll tell you what they are.
Let's understand this equation properly.
So y basically stands for your dependent variable
that you're going to predict.
B naught is the y intercept.
Now y intercept is nothing but this point here.
Now in this graph, you're basically
showing the relationship between your dependent variable y
and your independent variable x.
Now this is the linear relationship
between these two variables.
Okay, now your y intercept is basically
the point on the line
which starts at the y-axis.
This is y interceptor,
which is represented by B naught.
Now B one or beta is the slope of this line
now the slope can either be negative or positive,
depending on the relationship between the dependent
and independent variable.
The next variable that we have is x.
X here represents the independent variable
that is used to predict our resulting output variable.
Basically, x is used to predict the value of y.
Okay.
E here denotes the error in the computation.
For example, this is the actual line,
and these dots here represent the predicted values.
Now the distance between these two
is denoted by the error in the computation.
So this is the entire equation.
It's quite simple, right?
Linear regression will basically draw
a relationship between your input and your input variable.
That's how simple linear regression was.
Now to better understand linear regression,
I'll be running a demo in Python.
So guys, before I get started with our practical demo,
I'm assuming that most of you
have a good understanding of Python,
because explaining Python is going to be
out of the scope of today's session.
But if some of you are not familiar
with the Python language,
I'll leave a couple of links in the description box.
Those will be related to Python programming.
You can go through those links, understand Python,
and then maybe try to understand the demo.
But I'd be explaining the logic part of the demo in depth.
So the main thing that we're going to do here
is try and understand linear regression.
So it's okay if you do not understand Python for now.
I'll try to explain as much as I can.
But if you still want to understand this in a better way,
I'll leave a couple of links in the description box
you can go to those videos.
Let me just zoom in for you.
I hope all of you can see the screen.
Now in this linear regression demo,
what we're going to do is
we're going to form a linear relationship
between the maximum temperature
and minimum temperature on a particular date.
We're just going to do weather forecasting here.
So our task is to predict the maximum temperature,
taking input feature as minimum temperature.
So I'm just going to try and make you understand
linear regression through this demo.
Okay, we'll see how it actually works practically.
Before I get started with the demo,
let me tell you something about the data set.
Our data set is stored in this path basically.
The name of the data set is weather.csv.
Okay, now, this contains data on whether conditions
recorded on each day
at various weather stations around the world.
Okay, the information include precipitation,
snowfall, temperatures, wind speeds,
and whether the day included any thunderstorm
or other poor weather conditions.
So our first step in any demo for that matter
will be to import all the libraries that are needed.
So we're gonna begin our demo
by importing all the required libraries.
After that, we're going to read in our data.
Our data will be stored
in this variable called data set,
and we're going to use a read.csv function
since our data set is in the CSV format.
After that, I'll be showing you
how the data set looks.
We'll also look at the data set in depth.
Now let me just show you the output first.
Let's run this demo and see first.
We're getting a couple of plots which I'll
talk about in a while.
So we can ignore this warning.
It has nothing to do with...
So, first of all, we're printing the shape of our data set.
So, when we print the shape of our data set,
This is the output that we get.
So, basically, this shows that we have around
12,000 rows and 31 columns in our data set.
The 31 columns basically represent
the predictor variables.
So you can say that we have 31 predictor variables
in order to protect the weather conditions
on a particular date.
So guys, the main aim in this problem segment
is weather forecast.
We're going to predict the weather
by using a set of predictor variables.
So these are the different types
of predictor variables that we have.
Okay, we have something known as maximum temperature.
So this is what our data set looks like.
Now what I'm doing in this block of code is...
What we're doing is we're plotting our data points
on a 2D graph in order to understand our data set
and see if we can manually find any relationship
between the variables.
Here we've taken minimum temperature
and maximum temperature for doing our analysis.
So let's just look at this plot.
Before that, let me just comment all of these other plots,
so that you see on either graph that I'm talking about.
So, when you look at this graph,
this is basically the graph between your minimum temperature
and your maximum temperature.
Maximum temperature are dependent variable
that you're going to predict.
This is y.
And your minim temperature is your x.
It's basically your independent variable.
So if you look at this graph,
you can see that there is a sort of
linear relationship between the two,
except there are a little bit of outliers here and there.
There are a few data points which are a little bit random.
But apart from that, there is a pretty linear relationship
between your minimum temperature
and your maximum temperature.
So by this graphic, you can understand
that you can easily solve this problem
using linear regression,
because our data is very linear.
I can see a clear straight line over here.
This is our first graph.
Next, what I'm doing is I'm just checking
the average and maximum temperature that we have.
I'm just looking at the average of our output variable.
Okay.
So guys, what we're doing here right now
is just exploratory data analysis.
We're trying to understand our data.
We're trying to see the relationship
between our input variable and our output variable.
We're trying to see the mean or the average
of the output variable.
All of this is necessary to understand our data set.
So, this is what our average maximum temperature looks like.
So if we try to understand where exactly this is,
so our average maximum temperature
is somewhere between 28 and I would say between 30.
28 and 32, somewhere there.
So you can say that average maximum temperature
lies between 25 and 35.
And so that is our average maximum temperature.
Now that you know a little bit about the data set,
you know that there is a very good linear relationship
between your input variable and your output variable.
Now what you're going to do is you're going to
perform something known as data splicing.
Let me just comment that for you.
This section is nothing but data splicing.
So for those of you who are paying attention,
know that data splicing is nothing but
splitting your data set into training and testing data.
Now before we do that,
I mentioned earlier that we'll be only using two variables,
because we're trying to understand the relationship between
the minimum temperature and maximum temperature.
I'm doing this because I want you to understand
linear regression in the simplest way possible.
So guys, in order to make understand linear regression,
I have just derived only two variables from a data set.
Even though when we check the structure of a data set,
we had around 31 features,
meaning that we had 31 variables
which include my predictor variable and my target variable.
So, basically, we had 30 predictor variables
and we had one target variable,
which is your maximum temperature.
So, what I'm doing here is I'm only considering
these two variables,
because I want to show you exactly
how linear regression works.
So, here what I'm doing is I'm basically
extracting only these two variables
from our data set, storing it in x and y.
After that, I'm performing data splicing.
So here, I'm basically splitting the data
into training and testing data,
and remember one point that I am assigning
20% of the data to our testing data set,
and the remaining 80% is assigned for training.
That's how training works.
We assign maximum data set for training.
We do this because we want the machine learning model
or the machine learning algorithm to train better on data.
We wanted to take as much data as possible,
so that it can predict the outcome properly.
So, to repeat it again for you,
so here we're just splitting the data
into training and testing data set.
So, one more thing to note here is that
we're splitting 80% of the data from training,
and we're assigning the 20% of the data to test data.
The test size variable, this variable that you see,
is what is used to specify
the proportion of the test set.
Now after splitting the data into training and testing set,
finally, the time is to train our algorithm.
For that, we need to import the linear regression class.
We need to instantiate it
and call the fit method along with the training data.
This is our linear regression class,
and we're just creating an instance
of the linear regression class.
So guys, a good thing about Python is that
you have pre-defined classes for your algorithms,
and you don't have call your algorithms.
Instead, all you have to do,
is you call this class linear regression class,
and you have to create an instance of it.
Here I'm basically creating something known as a regressor.
And all you have to do is you have to call the fit method
along with your training data.
So this is my training data, x train and y train
contains my training data,
and I'm calling our linear regression instance,
which is regressor, along with this data set.
So here, basically, we're building the model.
We're doing nothing but building the model.
Now, one of the major things that
linear regression model does is
it finds the best value for the intercept and the slope,
which results in a line that best fits the data.
I've discussed what intercept and slope is.
So if you want to see the intercept and the slope
calculated by our linear regression model,
we just have to run this line of code.
And let's looks at the output for that.
So, our intercept is around 10.66
and our coefficient,
these are also known as beta coefficients,
coefficient are nothing but what we discussed, beta naught.
These are beta values.
Now this will just help you understand
the significance of your input variables.
Now what this coefficient value means is,
see, the coefficient value is around 0.92.
This means that for every one unit changed
of your minimum temperature,
the change in the maximum temperature is around 0.92.
This will just show you how significant
your input variable is.
So, for every one unit change in your minimum temperature,
the change in the maximum temperature
will be around 0.92.
I hope you've understood this part.
Now that we've trained our algorithm,
it's trying to make some predictions.
To do so, what we'll use is we'll use our test data set,
and we'll see how accurately our algorithm
predicts the percentage score.
Now to make predictions,
we have this line of code.
Predict is basically a predefined function in Python.
And all you're going to do is you're going to pass
your testing data set to this.
Now what you'll do is you'll compare
the actual output values,
which is basically stored in your y test.
And you'll compare these to the predicted values,
which is in y prediction.
And you'll store these comparisons in our data frame
called df.
And all I'm doing here is I'm printing the data frame.
So if you look at the output, this is what it looks like.
These are your actual values
and these are the values that you predicted
by building that model.
So, if your actual value is 28,
you predicted around 33,
here your actual value is 31,
meaning that your maximum temperature is 31.
And you predicted a maximum temperature of 30.
Now, these values are actually pretty close.
I feel like the accuracy is pretty good over here.
Now in some cases, you see a lot of variance, like 23.
Here it's 15.
Right here it's 22.
Here it's 11.
But such cases are very often.
And the best way to improve your accuracy I would say
is by training a model with more data.
Alright.
You can also view this comparison in the form of a plot.
Let's see how that looks.
So, basically, this is a bar graph
that shows our actual values and our predicted values.
Blue is represented by your actual values,
and orange is represented by your predicted values.
At places you can see that
we've predicted pretty well,
like the predictions are pretty close
to the actual values.
In some cases, the predictions are varying a little bit.
So in a few places, it is actually varying,
but all of this depends on your input data as well.
When we saw the input data,
also we saw a lot of variation.
We saw a couple of outliers.
So, all that also might effect your output.
But then this is how you build machine learning models.
Initially, you're never going to get
a really good accuracy.
What you should do is you have to improve
your training process.
That's the best way you can predict better,
either you use a lot of data,
train your model with a lot of data,
or you use other methods like parameter tuning,
or basically you try and find another predictor variable
that'll help you more in predicting your output.
To me, this looks pretty good.
Now let me show you another plot.
What we're doing is we're drawing a straight line plot.
Okay, let's see how it looks.
So guys, this straight line
represents a linear relationship.
Now let's say you get a new data point.
Okay, let's say the value of x is around 20.
So by using this line,
you can predict that four a minimum temperature of 20,
your maximum temperature would be around 25
or something like that.
So, we basically drew a linear relationship
between our input and output variable over here.
And the final step is to evaluate
the performance of the algorithm.
This step is particularly important to compare
how well different algorithms perform
on a particular data set.
Now for regression algorithms,
three evaluation metrics are used.
We have something known as mean absolute error,
mean squared error, and root mean square error.
Now mean absolute error is nothing but
the absolute value of the errors.
Your mean squared error is a mean of the squared errors.
That's all.
It's basically you read this and you understand
what the error means.
A root mean squared error is the square root
of the mean of the squared errors.
Okay.
So these are pretty simple to understand
your mean absolute error, your mean squared errors,
your root mean squared error.
Now, luckily, we don't have to perform these
calculations manually.
We don't have to code each of these calculations.
The cycle on library comes with prebuilt functions
that can be used to find out these values.
Okay.
So, when you run this code, you will get
these values for each of the errors.
You'll get around 3.19 as the mean absolute error.
Your mean squared error is around 17.63.
Your root mean squared error is around 4.19.
Now these error values basically show that
our model accuracy is not very precise,
but it's still able to make a lot of predictions.
We can draw a good linear relationship.
Now in order to improve the efficiency at all,
there are a lot of methods like this,
parameter tuning and all of that,
or basically you can train your model with a lot more data.
Apart from that, you can use other predictor variables,
or maybe you can study the relationship between
other predictor variables
and your maximum temperature variable.
There area lot of ways
to improve the efficiency of the model.
But for now, I just wanted to make you understand
how linear regression works,
and I hope all of you have a good idea about this.
I hope all of you have a good understanding
of how linear regression works.
This is a small demo about it.
If any of you still have any doubts,
regarding linear regression,
please leave that in the comment section.
We'll try and solve all your errors.
So, if you look at this equation,
we calculated everything here.
we drew a relationship between y and x,
which is basically x was our minimum temperature,
y was our maximum temperature.
We also calculated the slope and the intercept.
And we also calculated the error in the end.
We calculated mean squared error
we calculated the root mean squared error.
We also calculate the mean absolute error.
So that was everything about linear regression.
This was a simple linear regression model.
Now let's move on and look at our next algorithm,
which is a logistic regression.
Now, in order to understand why we use logistic regression,
let's consider a small scenarios.
Let's say that your little sister
is trying to get into grad school
and you want to predict whether she'll get admitted
in her dream school or not.
Okay, so based on her CGPA and the past data,
you can use logistic regression
to foresee the outcome.
So logistic regression will allow you to analyze
the set of variables and predict a categorical outcome.
Since here we need to predict whether she will
get into a school or not,
which is a classification problem,
logistic regression will be used.
Now I know the first question in your head is,
why are we not using linear regression in this case?
The reason is that linear regression
is used to predict a continuous quantity,
rather than a categorical one.
Here we're going to predict
whether or not your sister is going to get into grad school.
So that is clearly a categorical outcome.
So when the result in outcome
can take only classes of values,
like two classes of values,
it is sensible to have a model that predicts the value
as either zero or one,
or in a probability form that ranges between zero and one.
Okay.
So linear regression does not have this ability.
If you use linear regression
to model a binary outcome,
the resulting model will not predict y values
in the range of zero and one,
because linear regression works on
continuous dependent variables,
and not on categorical variables.
That's why we make use of logistic regression.
So understand that linear regression was used
to predict continuous quantities,
and logistic regression is used to
predict categorical quantities.
Okay, now one major confusion that everybody has
is people keep asking me
why is logistic regression called logistic regression
when it is used for classification.
The reason it is named logistic regression
is because its primary technique
is very similar to logistic regression.
There's no other reason behind the naming.
It belongs to the general linear models.
It belongs to the same class as linear regression,
but that is not the other reason
behind the name logistic regression.
Logistic regression is mainly used
for classification purpose,
because here you'll have to predict a dependent variable
which is categorical in nature.
So this is mainly used for classification.
So, to define logistic regression for you,
logistic regression is a method used to predict
a dependent variable y,
given an independent variable x,
such that the dependent variable is categorical,
meaning that your output is a categorical variable.
So, obviously, this is classification algorithm.
So guys, again, to clear your confusion,
when I say categorical variable,
I mean that it can hold values like one or zero,
yes or no, true or false, and so on.
So, basically, in logistic regression,
the outcome is always categorical.
Now, how does logistic regression work?
So guys, before I tell you how logistic regression works,
take a look at this graph.
Now I told you that the outcome
in a logistic regression is categorical.
Your outcome will either be zero or one,
or it'll be a probability that ranges between zero and one.
So, that's why we have this S curve.
Now some of you might think that why do we have an S curve.
We can obviously have a straight line.
We have something known as a sigmoid curve,
because we can have values ranging between zero and one,
which will basically show the probability.
So, maybe your output will be 0.7,
which is a probability value.
If it is 0.7,
it means that your outcome is basically one.
So that's why we have this sigmoid curve like this.
Okay.
Now I'll explain more about this
in depth in a while.
Now, in order to understand how logistic regression works,
first, let's take a look at
the linear regression equation.
This was the logistic regression equation
that we discussed.
Y here stands for the dependent variable
that needs to be predicted
beta naught is nothing by the y intercept.
Beta one is nothing but the slope.
And X here represents the independent variable
that is used to predict y.
That E denotes the error on the computation.
So, given the fact that x is the independent variable
and y is the dependent variable,
how can we represent a relationship between x an y
so that y ranges only between zero and one?
Here this value basically denotes
probably of y equal to one,
given some value of x.
So here, because this Pr, denotes probability
and this value basically denotes that the probability
of y equal to one, given some value of x,
this is what we need to find out.
Now, if you wanted to calculate the probability
using the linear regression model,
then the probability will look something like
P of X equal to beta naught
plus beta one into X.
P of X will be equal to beta naught plus beta one into X,
where P of X nothing but
your probability of getting y equal to one,
given some value of x.
So the logistic regression equation
is derived from the same equation,
except we need to make a few alterations,
because the output is only categorical.
So, logistic regression does not necessarily calculate
the outcome as zero or one.
I mentioned this before.
Instead, it calculates the probability of a variable
falling in the class zero or class one.
So that's how we can conclude that
the resulting variable must be positive,
and it should lie between zero and one,
which means that it must be less than one.
So to meet these conditions,
we have to do two things.
First, we can take the exponent of the equation,
because taking an exponential of any value
will make sure that you get a positive number.
Correct?
Secondly, you have to make sure
that your output is less than one.
So, a number divided by itself plus one
will always be less than one.
So that's how we get this formula
First, we take the exponent of the equation,
beta naught plus beta one plus x
and then we divide it by that number plus one.
So this is how we get this formula.
Now the next step is to calculate
something known as a logic function.
Now the logic function is nothing,
but it is a link function
that is represented as an S curve
or as a sigmoid curve
that ranges between the value zero and one.
It basically calculates the probability
of the output variable.
So if you look at this equation, it's quite simple.
What we have done here is we just cross multiply
and take each of our beta naught
plus beta one into x as common.
The RHS denotes the linear equation for
the independent variables.
The LHS represents the odd ratio.
So if you compute this entire thing,
you'll get this final value,
which is basically your logistic regression equation.
Your RHS here denotes the linear equation
for independent variables,
and your LHS represents the odd ratio
which is also known as the logic function.
So I told you that logic function
is basically a function that represents an S curve
that bring zero and one.
this will make sure that our value
ranges between zero and one.
So in logistic regression,
on increasing this X by one measure,
it changes the logic by a factor of beta naught.
It's the same thing as I showed you in logistic regression.
So guys, that's how you derive
the logistic regression equation.
So if you have any doubts regarding these equations,
please leave them in the comment section,
and I'll get back to you, and I'll clear that out.
So to sum it up, logistic regression is used
for classification.
The output variable will always be a categorical variable.
We also saw how you derive the logistic regression equation.
And one more important thing is that
the relationship between the variables
and a logistic regression is denoted as
an S curve which is also knows as a sigmoid curve,
and also the outcome does not
necessarily have to be calculated as zero or one.
It can be calculate as a probability
that the output lies in class one or class zero.
So your output can be a probability
ranging between zero and one.
That's why we have a sigmoid curve.
So I hope all of you are clear with logistic regression.
Now I won't be showing you the demo right away.
I'll explain a couple of more classification algorithms.
Then I'll show you a practical demo
where we'll use multiple classification algorithms
to solve the same problem.
Again, we'll also calculate the accuracy
and se which classification algorithm is doing the best.
Now the next algorithm I'm gonna talk about
is decision tree.
Decision tree is one of my favorite algorithms,
because it's very simple to understand
how a decision tree works.
So guys, before this, we discussed linear regression,
which was a regression algorithm.
Then we discussed logistic regression,
which is a classification algorithm.
Remember, don't get confused just because
it has the name logistic regression.
Okay, it is a classification algorithm.
Now we're discussing decision tree,
which is again a classification algorithm.
Okay.
So what exactly is a decision tree?
Now a decision tree is, again,
a supervised machine learning algorithm
which looks like an inverted tree
wherein each node represents a predictor variable,
and the link between the node represents a decision,
and each leaf node represents an outcome.
Now I know that's a little confusing,
so let me make you understand what a decision tree is
with the help of an example.
Let's say that you hosted a huge party,
and you want to know how many of your gusts
are non-vegetarians.
So to solve this problem,
you can create a simple decision tree.
Now if you look at this figure over here,
I've created a decision tree that classifies a guest
as either vegetarian or non-vegetarian.
Our last outcome here is non-veg or veg.
So here you understand
that this is a classification algorithm,
because here you're predicting a categorical value.
Each node over here represents a predictor variable.
So eat chicken is one variable,
eat mutton is one variable,
seafood is another variable.
So each node represents a predictor variable
that will help you conclude whether or not
a guest is a non-vegetarian.
Now as you traverse down the tree,
you'll make decisions that each node
until you reach the dead end.
Okay, that's how it works.
So, let's say we got a new data point.
Now we'll pass it through the decision tree.
The first variable is did the guest
eat the chicken?
If yes, then he's a non-vegetarian.
If no, then you'll pass it to the next variable,
which is did the guest eat mutton?
If yes, then he's a non-vegetarian.
If no, then you'll pass it to the next variable,
which is seafood.
If he ate seafood, then he is a non-vegetarian.
If no, then he's a vegetarian.
this is how a decision tree works.
It's a very simple algorithm
that you can easily understand.
It has drawn out letters, which is very easy to understand.
Now let's understand the structure of a decision tree.
I just showed you an example
of how the decision tree works.
Now let me take the same example
and tell you the structure for decision tree.
So, first of all, we have something known as the root node.
Okay.
The root node is the starting point
of a decision tree.
Here you'll perform the first split
and split it into two other nodes
or three other nodes, depending on your problem statement.
So the top most node is known as your root node.
Now guys, about the root node,
the root node is assigned to a variable
that is very significant,
meaning that that variable is very important
in predicting the output.
Okay, so you assign a variable
that you think is the most significant at the root node.
After that, we have something known as internal nodes.
So each internal node represents a decision point
that eventually leads to the output.
Internal nodes will have other predictor variables.
Each of these are nothing predictor variables.
I just made it into a question
otherwise these are just predictor variables.
Those are internal nodes.
Terminal nodes, also known as the leaf node,
represent the final class of the output variable,
because these are basically your outcomes,
non-veg and vegetarian.
Branches are nothing but connections between nodes.
Okay, these connections are links between
each node is known as a branch,
and they're represented by arrows.
So each branch will have some response to it,
either yes or no, true or false, one or zero, and so on.
Okay.
So, guys, this is the structure of a decision tree.
It's pretty understandable.
Now let's move on and
we'll understand how the decision tree algorithm works.
Now there are many ways to build a decision tree,
but I'll be focusing on something known
as the ID3 algorithm.
Okay, this is something known as the ID3 algorithm.
That is one of the ways in which you can build
the decision tree.
ID3 stands for Iterative Dichotomiser 3 algorithm,
which is one of the most effective algorithms
used to build a decision tree.
It uses the concepts of entropy and information gain
in order to build a decision tree.
Now you don't have to know what exactly
the ID3 algorithm is.
It's just a concept behind building a decision tree.
Now the ID3 algorithm has around six defined steps
in order to build a decision tree.
So the first step is you will select the best attribute.
Now what do you mean by the best attribute?
So, attribute is nothing but
the predictor variable over here.
So you'll select the best predictor variable.
Let's call it A.
After that, you'll assign this A
as a decision variable for the root node.
Basically, you'll assign this predictor variable A
at the root node.
Next, what you'll do is for each value of A,
you'll build a descendant of the node.
Now these three steps, let's look at it
with the previous example.
Now here the best attribute is eat chicken.
Okay, this is my best attribute variable over here.
So I selected that attribute.
And what is the next step?
Step two was assigned that as a decision variable.
So I assigned eat chick as the decision variable
at the root node.
Now you might be wondering how do I know
which is the best attribute.
I'll explain all of that in a while.
So what we did is we assigned this other root node.
After that, step number three says for each value of A,
build a descendant of the node.
So for each value of this variable,
build a descendant node.
So this variable can take two values, yes and no.
So for each of these values,
I build a descendant node.
Step number four, assign classification labels
to the leaf node.
To your leaf node, I have assigned
classification one as non-veg, and the other is veg.
That is step number four.
Step number five is if data is correctly classified,
then you stop at that.
However, if it is not,
then you keep iterating over the tree,
and keep changing the position of
the predictor variables in the tree,
or you change the root node also
in order to get the correct output.
So now let me answer this question.
What is the best attribute?
What do you mean by the best attribute
or the best predictor variable?
Now the best attribute is the one
that separates the data into different classes,
most effectively, or it is basically
a feature that best splits the data set.
Now the next question in your head must be how do I decide
which variable or which feature best splits the data.
To do this, there are two important measures.
There's something known as information gain
and there's something known as entropy.
Now guys, in order to understand
information gain and entropy,
we look at a simple problem statement.
This data represents the speed of a car
based on certain parameters.
So our problem statement here is to study the data set
and create a decision tree that classifies
the speed of the car as either slow or fast.
So our predictor variables here are road type,
obstruction, and speed limit,
and or response variable, or our output variable is speed.
So we'll be building a decision tree using these variables
in order to predict the speed of car.
Now like I mentioned earlier,
we must first begin by deciding a variable
that best splits the data set
and assign that particular variable to the root node
and repeat the same thing for other nodes as well.
So step one, like we discussed earlier,
is to select the best attribute A.
Now, how do you know which variable best separates the data?
The variable with the highest information gain
best derives the data into the desired output classes.
First of all, we'll calculate two measures.
We'll calculate the entropy and the information gain.
Now this is where it ell you what exactly entropy is,
and what exactly information gain is.
Now entropy is basically used to measure
the impurity or the uncertainty present in the data.
It is used to decide how a decision tree can split the data.
Information gain, on the other hand,
is the most significant measure
which is used to build a decision tree.
It indicates how much information a particular variable
gives us a bout the final outcome.
So information gain is important,
because it is used to choose a variable
that best splits the data at each node
for a decision tree.
Now the variable with the highest information gain
will be used to split the data at the root node.
Now in our data set, there are are four observations.
So what we're gonna do is we'll start by calculating
the entropy and information gain
for each of the predictor variable.
So we're gonna start by calculating the information gain
and entropy for the road type variable.
In our data set, you can see that
there are four observations.
There are four observations in the road type column,
which corresponds to the four labels in the speed column.
So we're gonna begin by calculating the information gain
of the parent node.
The parent node is nothing but the speed of the care node.
This is our output variable, correct?
It'll be used to show whether the speed of the car
is slow or fast.
So to find out the information gain of the
speed of the car variable,
we'll go through a couple of steps.
Now we know that there are four observations
in this parent node.
First, we have slow.
Then again we have slow, fast, and fast.
Now, out of these four observations, we have two classes.
So two observations belong to the class slow,
and two observations belong to the class fast.
So that's how you calculate P slow and P fast.
P slow is nothing by the fraction
of slow outcomes in the parent node,
and P fast is the fraction of fast outcomes
in the parent node.
And the formula to calculate P slow
is the number of slow outcomes in the parent node
divided by the total number of outcomes.
So the number of slow outcomes in the parent node is two,
and the total number of outcomes is four.
We have four observations in total.
So that's how we get P of slow as 0.5.
Similarly, for P of fast, you'll calculate
the number of fast outcomes
divided by the total number of outcomes.
So again, two by four, you'll get 0.5.
The next thing you'll do is you'll calculate
the entropy of this node.
So to calculate the entropy, this is the formula.
All you have to do is you have to substitute the,
you'll have to substitute the value in this formula.
So P of slow we're substituting as 0.5.
Similarly, P of fast as 0.5.
Now when you substitute the value,
you'll get a answer of one.
So the entropy of your parent node is one.
So after calculating the entropy of the parent node,
we'll calculate the information gain of the child node.
Now guys, remember that if the information gain
of the road type variable is great than the information gain
of all the other predictor variables,
only then the root node can be split by using
the road type variable.
So, to calculate the information gain of road type variable,
we first need to split the root node
by sing the road type variable.
We're just doing this in order to check
if the road type variable
is giving us maximum information about a data.
Okay, so if you notice that road type has two outcomes,
it has two values, either steep or flat.
Now go back to our data set.
So here what you can notice is
whenever the road type is steep,
so first what we'll do is we'll check
the value of speed that we get
when the road type is steep.
So, first, observation.
You see that whenever the road type is steep,
you're getting a speed of slow.
Similarly, in the second observation,
when the road type is steep,
you'll get a value of slow again.
If the road type is flat, you'll get an observation of fast.
And again, if it is steep, there is a value of fast.
So for three steep values,
we have slow, slow, and fast.
And when the road type is flat,
we'll get an output of fast.
That's exactly what I've done in this decision tree.
So whenever the road type is steep,
you'll get slow, slow or fast.
And whenever the road type is flat,
you'll get fast.
Now the entropy of the right-hand side is zero.
Entropy is nothing but the uncertainty.
There's no uncertainty over here.
Because as soon as you see that the road type is flat,
your output is fast.
So there's no uncertainty.
But when the road type is steep,
you can have any one of the following outcomes,
either your speed will be slow
or it can be fast.
So you'll start by calculating the entropy
of both RHS and LHS of the decision tree.
So the entropy for the right side child node will be zero,
because there's no uncertainty here.
Immediately, if you see that the road type is flat,
your speed of the car will be fast.
Okay, so there's no uncertainty here,
and therefore your entropy becomes zero.
Now entropy for the left-hand side
is we'll again have to calculate
the fraction of P slow and the fraction of P fast.
So out of three observations,
in two observations we have slow.
That's why we have two by three over here.
Similarly for P fast,
we have one P fast
divided by the total number of observation which are three.
So out of these three, we have two slows and one fast.
When you calculate P slow and P fast,
you'll get these two values.
And then when you substitute the entropy in this formula,
you'll get the entropy as 0.9 for the road type variable.
I hope you all are understanding this.
I'll go through this again.
So, basically, here we are calculating
the information gain and entropy for road type variable.
Whenever you consider road type variable,
there are two values, steep and flat.
And whenever the value for road type is steep,
you'll get anyone of these three outcomes,
either you'll get slow, slow, or fast.
And when the road type is flat,
your outcome will be fast.
Now because there is no uncertainty
whenever the road type is flat,
you'll always get an outcome of fast.
This means that the entropy here is zero,
or the uncertainty value here is zero.
But here, there is a lot of uncertainty.
So whenever your road type is steep,
your output can either be slow or it can be fast.
So, finally, you get the Python as 0.9.
So in order to calculate the information gain
of the road type variable.
You need to calculate the weighted average.
I'll tell you why.
In order to calculate the information gain,
you need to know the entropy of the parent,
which we calculate as one,
minus the weighted average into the entropy
of the children.
Okay.
So for this formula, you need to calculate
all of these values.
So, first of all, you need to calculate the entropy
of the weighted average.
Now the total number of outcomes in the parent node
we saw were four.
The total number of outcomes
in the left child node were three.
And the total number of outcomes in the right child node
was one.
Correct?
In order to verify this with you,
the total number of outcomes in the parent node are four.
One, two, three, and four.
Coming to the child node, which is the road type,
the total number of outcomes on the right-hand side
of the child node is one.
And the total number of outcomes
on the left-hand side of the child node is three.
That's exactly what I've written over here.
Alright, I hope you all understood these three values.
After that, all you have to do is
you have to substitute these values in this formula.
So when you do that, you'll get
the entropy of the children with weighted average
will be around 0.675.
Now just substitute the value in this formula.
So if you calculate the information gain
of the road type variable,
you'll get a value of 0.325.
Now by using the same method,
you're going to calculate the information gain
for each of the predictor variable,
for road type, for obstruction, and for speed limit.
Now when you follow the same method
and you calculate the information gain,
you'll get these values.
Now what does this information gain for road type
equal to 0.325 denote?
Now the value 0.325 for road type denotes that
we're getting very little information gain
from this road type variable.
And for obstruction, we literally have
information gain of zero.
Similarly, information gained for speed limit is one.
This is the highest value we've got for information gain.
This means that we'll have to use the speed limit variable
at our root node in order to split the data set.
So guys, don't get confused whichever variable
gives you the maximum information gain.
That variable has to be chosen at the root node.
So that's why we have the root node as speed limit.
So if you've maintained the speed limit,
then you're going to go slow.
But if you haven't maintained the speed limit,
then the speed of your car is going to be fast.
Your entropy is literally zero,
and your information is one,
meaning that you can use this variable at your root node
in order to split the data set,
because speed limit gives you the maximum information gain.
So guys, I hope this use case is clear to all of you.
To sum everything up,
I'll just repeat the entire thing to you all once more.
So basically, here you were given a problem statement
in order to create a decision tree
that classifies the speed of a car as either slow or fast.
So you were given three predictor variables
and this was your output variable.
Information gained in entropy are basically two measures
that are used to decide which variable
will be assigned to the root node of a decision tree.
Okay.
So guys, as soon as you look at the data set,
if you compare these two columns,
that is speed limit and speed,
you'll get an output easily.
Meaning that if you're maintaining speed limit,
you're going to go slow.
But if you aren't maintaining speed limit,
you're going to a fast.
So here itself we can understand the speed limit
has no uncertainty.
So every time you've maintained your speed limit,
you will be going slow,
and every time your outside or speed limit,
you will be going fast.
It's as simple as that.
So how did you start?
So you started by calculating
the entropy of the parent node.
You calculated the entropy of the parent node,
which came down to one.
Okay.
After that, you calculated the information gain
of each of the child nodes.
In order to calculate
the information gain of the child node,
you stat by calculating the entropy
of the right-hand side and the left-hand side
of the decision tree.
Okay.
Then you calculate the entropy
along with the weighted average.
You substitute these values in the information gain formula,
and you get the information gain
for each of the predictor variables.
So after you get the information gain
of each of the predictor variables,
you check which variable gives you
the maximum information gain,
and you assign that variable to your root node.
It's as simple as that.
So guys, that was all about decision trees.
Now let's look at our next classification algorithm
which is random forest.
Now first of all, what is a random forest?
Random forest basically builds multiple decision trees
and glues them together to get a more accurate
and stable prediction.
Now if already have decision trees
and random forest is nothing but
a collection of decision tree,
why do we have to use a random forest
when we already have decision tree?
There are three main reasons why random forest is used.
Now even though decision trees are convenient
and easily implemented,
they are not as accurate as random forest.
Decision trees work very effectively
with the training data,
backup they're not flexible
when it comes to classifying anew sample.
Now this happens because of something known as overfitting.
Now overfitting is a problem
that is seen with decision trees.
It's something that commonly occurs
when we use decision trees.
Now overfitting occurs when a model studies
a training data to such an extent
that it negatively influences
the performance of the model on a new data.
Now this means that the disturbance
in the training data is recorded,
and it is learned as concept by the model.
If there's any disturbance
or any thought of noise in the training data
or any error in the training data,
that is also studied by the model.
The problem here is that these concepts
do not apply to the testing data,
and it negatively impacts the model's ability
to classify new data.
So to sum it up,
overfitting occurs whenever your model
learns the training data,
along with all the disturbance in the training data.
So it basically memorized the training data.
And whenever a new data will be given to your model,
it will not predict the outcome very accurately.
now this is a problem seen in decision trees.
Okay.
But in random forest, there's something known as bagging.
Now the basic idea behind bagging is
to reduce the variations and the predictions
by combining the result of multiple decision trees
on different samples of the data set.
So your data set will be divided into different samples,
and you'll be building a decision tree
on each of these samples.
This way, each decision tree will be studying
one subset of your data.
So this way over fitting will get reduced
because one decision tree is not studying
the entire data set.
Now let's focus on random forest.
Now in order to understand random forest,
we look at a small example.
We can consider this data set.
In this data, we have four predictor variables.
We have blood flow, blocked arteries,
chest pain, and weight.
Now these variables are used to predict
whether or not a person has a heart disease.
So we're going to use this data set
to create a random forest that predicts
if a person has a heart disease or not.
Now the first step in creating a random forest
is that you create a bootstrap data set.
Now in bootstrapping, all you have to do
is you have to randomly select samples
from your original data set.
Okay.
And a point to note is that you can select the same sample
more than once.
So if you look at the original data set,
we have a abnormal, normal, normal, and abnormal.
Look at the blood flow section.
Now here I've randomly selected samples,
normal, abnormal,
and I've selected one sample twice.
You can do this in a bootstrap data set.
Now all I did here is
I created a bootstrap data set.
Boot strapping is nothing but an estimation method
used to make predictions on a data
by re-sampling the data.
This is a bootstrap data set.
Now even though this seems very simple,
in real world problems,
you'll never get such small data set.
Okay, so bootstrapping
is actually a little more complex than this.
Usually in real world problems,
you'll have a huge data set,
and bootstrapping that data set is actually
a pretty complex problem.
I'm here because I'm making you understand
how random forest works,
so that's why I've considered a small data set.
Now you're going to use the bootstrap data set
that you created,
and you're going to build decision trees from it.
Now one more thing to note in random forest is
you will not be using your entire data set.
Okay, so you'll only be using few other variables
at each node.
So, for example, we'll only consider two variables
at each step.
So if you begin at the root node here,
we will randomly select two variables
as candidates for the root node.
Okay, let's say that we selected blood flow
and blocked arteries.
Out of these two variables we have to select the variable
that best separates the sample.
Okay.
So for the sake of this example,
let's say that blocked arteries
is the most significant predictor,
and that's why we'll assign it to the root node.
Now our next step is to repeat the same process
for each of these upcoming branch nodes.
Here we'll again select two variables at random
as candidates for each of these branch nodes,
and then choose a variable
that best separates the samples, right?
So let me just repeat this entire process.
So you know that you start creating a decision tree
by selecting the root node.
In random forest, you'll randomly select
a couple of variables for each node,
and then you'll calculate which variable
best splits the data at that node.
So for each node, we'll randomly select
two or three variables.
And out of those two, three variables,
we'll see which variable best separates the data.
Okay, so at each node,
we'll because calculating information gain an entropy.
Basically, that's what I mean.
At every node, you'll calculate information gain
and entropy of two or three variables,
and you'll see which variable
has the highest information gain,
and you'll keep descending downwards.
That's how you create a decision tree.
So we just created our first decision tree.
Now what you do is you'll go back to step one,
and you'll repeat the entire process.
So each decision tree will predict the output class
based on the predictor variables
that you've assigned to each decision tree.
Now let's say for this decision tree,
you've assigned blood flow.
Here we have blocked arteries at the root node.
Here we might have blood flow at the root node and so on.
So your output will depend on which predictor variable
is at the root node.
So each decision tree will predict the output class
based on the predictor variable
that you assigned in that tree.
Now what you do is you'll go back to step one,
you'll create a new bootstrap data set,
and then again you'll build a new decision tree.
And for that decision tree,
you'll consider only a subset of variables,
and you'll choose the best predictor variable
by calculating the information gain.
So you will keep repeating this process.
So you just keep repeating step two and step one.
Okay.
And you'll keep creating multiple decision trees.
Okay.
So having a variety of decision trees in a random forest
is what makes it more effective than
an individual decision tree.
So instead of having an individual decision tree,
which is created using all the features,
you can build a random forest
that uses multiple decision trees
wherein each decision tree has a random set
of predictor variables.
Now step number four is predicting the outcome
of a new data point.
So now that you've created a random forest,
let's see how it can be used
to predict whether a new patient has a heart disease or not.
Okay, now this diagram basically has a data
about the new patient.
Okay, this is the data about the new patient.
He doesn't have blocked arteries.
He has chest pain, and his weight is around 185 kgs.
Now all you have to do is you have to run this data
down each of the decision trees that you made.
So, the first decision tree shows that
yes, this person has heart disease.
Similarly, you'll run the information of this new patient
through every decision tree that you created.
Then depending on how many votes you get for yes and no,
you'll classify that patient
as either having heart disease or not.
All you have to do is you have to run
the information of the new patient
through all the decision trees that you created
in the previous step,
and the final output is based on the number of votes
each of the class is getting.
Okay, let's say that three decision trees
said that yes the patient has heart disease,
and one decision tree said that no it doesn't have.
So this means you will obviously classify
the patient as having a heart disease
because three of them voted for yes.
It's based on majority.
So guys, I hope the concept behind random forest
is understandable.
Now the next step is you will evaluate
the efficiency of the model.
Now earlier when we created the bootstrap data set
we left out one entry sample.
This is the entry sample we left out,
because we repeated one sample twice.
If you'll remember in the bootstrap data set,
here we repeated an entry twice,
and we missed out on one of the entries.
We missed out on one of the entries.
So what we're gonna do is...
So for evaluating the model,
we'll be using the data entry that we missed out on.
Now in a real world problem,
about 1/3 of the original data set is not included
in the bootstrap dataset.
Because there's a huge amount of data
in a real world problem,
so 1/3 of the original data set
is not included in the bootstrap data set.
So guys, the sample data set
which is not there in your bootstrap data set
is known as out-of-bag data set,
because basically this is our out-of-bag data set.
Now the out-of-bag data set
is used to check the accuracy of the model.
Because the model was not created
by using the out-of-bag data set,
it will give us a good understanding
of whether the model is effective or not.
Now the out-of-bag data set
is nothing but your testing data set.
Remember, in machine learning, there's training
and testing data set.
So your out-of-bag data set
is nothing but your testing data set.
This is used to evaluate the efficiency of your model.
So eventually, you can measure the accuracy
of a random forest by the proportion
of out-of-bag samples that are correctly classified,
because the out-of-bag data set
is used to evaluate the efficiency of your model.
So you can calculate the accuracy
by understanding how many samples
or was this out-of-bag data set
correctly able to classify it.
So guys, that was an explanation about
how random forest works.
To give you an overview,
let me just run you through all the steps that we took.
So basically, this was our data set,
and all we have to do is we have to predict
whether a patient has heart disease or not.
So, our first step was to create a bootstrap data set.
A bootstrap data set is nothing but randomly selected
observations from your original data set,
and you can also have duplicate values
in your bootstrap data set.
Okay.
The next step is you're going to create a decision tree
by considering a random set of predictor variables
for each decision tree.
Okay.
So, the third step is you'll go back to step one,
create a bootstrap data set.
Again, create a decision tree.
So this iteration is performed hundreds of times
until you are multiple decision trees.
Now that you've created a random forest,
you'll use this random forest to predict the outcome.
So if you're given a new data point
and you have to classify it
into one of the two classes,
we'll just run this new information
through all the decision trees.
And you'll just take the majority
of the output that you're getting from the decision trees
as your outcome.
Now in order to evaluate the efficiency of the model,
you'll use the out of the bag sample data set.
Now the out-of-bag sample is basically the sample
that was not included in your bootstrap data set,
but this sample is coming
from your original data set, guys.
This is not something that you randomly create.
This data set was there in your original data set,
but it was just not mentioned
in your bootstrap data set.
So you'll use your out-of-bag sample
in order to calculate the accuracy
of your random forest.
So the proportion of out-of-bag samples
that are correctly classified will give you the accuracy
of your model.
So that is all for random forest.
So guys, I'll discuss other
classification algorithms with you,
and only then I'll show you a demo on
the classification algorithms.
Now our next algorithm is something known as naive Bayes.
Naive Bayes is, again,
a supervised classification algorithm,
which is based on the Bayes Theorem.
Now the Bayes Theorem basically follows
a probabilistic approach.
The main idea behind naive Bayes is that
the predictor variables in a machine learning model
are independent of each other,
meaning that the outcome of a model
depends on a set of independent variables
that have nothing to do with each other.
Now a lot of you might ask why is naive Bayes
called naive.
Now usually, when I tell anybody why naive Bayes,
they keep asking me why is naive Bayes called naive.
So in real world problems predictor variables
aren't always independent of each other.
There is always some correlation
between the independent variables.
Now because naive Bayes considers each predictor variable
to be independent of any other variable in the model,
it is called naive.
This is an assumption that naive Bayes states.
Now let's understand the math
behind the naive Bayes algorithm.
So like I mentioned, the principle behind naive Bayes
is the Bayes Theorem,
which is also known as the Bayes Rule.
The Bayes Theorem is used to calculate
the conditional probability,
which is nothing but the probability of an event occurring
based on information about the events in the past.
This is the mathematical equation for the Bayes Theorem.
Now, in this equation, the LHS is nothing
but the conditional probability of event A occurring,
given the event B.
P of A is nothing but probability of event A occurring
P of B is probability of event B.
And PB of A is nothing but the conditional probability
of event B occurring, given the event A.
Now let's try to understand how naive Bayes works.
Now consider this data set of
around thousand 500 observations.
Okay, here we have the following output classes.
We have either cat, parrot, or turtle.
These are our output classes,
and the predictor variables are
swim, wings, green color, and sharp teeth.
Okay.
So, basically, your type is your output variable,
and swim, wings, green, and sharp teeth
are your predictor variables.
Your output variables has three classes,
cat, parrot, and turtle.
Okay.
Now I've summarized this table I've shown on the screen.
The first thing you can see is the class of type cats
shows that out of 500 cats,
450 can swim,
meaning that 90% of them can.
And zero number of cats have wings,
and zero number of cats are green in color,
and 500 out of 500 cats have sharp teeth.
Okay.
Now, coming to parrot, it says 50 out of 500 parrots
have true value for swim.
Now guys, obviously, this does not hold true
in real world.
I don't think there are any parrots who can swim,
but I've just created this data set
so that we can understand naive Bayes.
So, meaning that 10% of parrots have true value for swim.
Now all 500 parrots have wings,
and 400 out of 500 parrots are green in color,
and zero parrots have sharp teeth.
Coming to the turtle class,
all 500 turtles can swim.
Zero number of turtles have wings.
And out of 500, hundred turtles are green in color,
meaning that 20% of the turtles are green in color.
And 50 out of 500 turtles have sharp teeth.
So that's what we understand from this data set.
Now the problem here is
we are given our observation over here,
given some value for swim, wings, green, and sharp teeth.
What we need to do is we need to predict
whether the animal is a cat, parrot, or a turtle,
based on these values.
So the goal here to predict whether it is a cat,
parrot, or a turtle
based on all these defined parameters.
Okay.
Based on the value of swim, wings, green, and sharp teeth,
we'll understand whether the animal is a cat,
or is it a parrot, or is it a turtle.
So, if you look at the observation,
the variables swim and green have a value of true,
and the outcome can be anyone of the types.
It can either be a cat, it can be a parrot,
or it can be a turtle.
So in order to check if the animal is a cat,
all you have to do is you have to calculate
the conditional probability at each step.
So here what we're doing is
we need to calculate the probability that
this is a cat,
given that it can swim and it is green in color.
First, we'll calculate the probability that it can swim,
given that it's a cat.
And two, the probability that it is green
and the probability of it being green,
given that it is a cat,
and then we'll multiply it
with the probability of it being a cat
divided by the probability of swim and green.
Okay.
So, guys, I know you all can calculate the probability.
It's quite simple.
So once you calculate the probability here,
you'll get a direct value of zero.
Okay, you'll get a value of zero,
meaning that this animal is definitely not a cat.
Similarly, if you do this for parrots,
you calculate a conditional probability,
you'll get a value of 0.0264
divided by probability of swim comma green.
We don't know this probability.
Similarly, if you check this for the turtle,
you'll get a probability of 0.066
divided by P swim comma green.
Okay.
Now for these calculations, the denominator is the same.
The value of the denominator is the same,
and the value of and the probability of it
being a turtle is greater than that of a parrot.
So that's how we can correctly predict
that the animal is actually a turtle.
So guys, this is how naive Bayes works.
You basically calculate
the conditional probability at each step.
Whatever classification needs to be done,
that has to be calculated through probability.
There's a lot of statistic
that comes into naive Bayes.
And if you all want to learn more about statistics
and probability,
I'll leave a link in the description.
You all can watch that video as well.
There I've explain exactly
what conditional probability is,
and the Bayes Theorem is also explained very well.
So you all can check out that video also.
And apart from this, if you all have any doubts
regarding any of the algorithms,
please leave them in the comment section.
Okay, I'll solve your doubts.
And apart from that, I'll also leave a couple of links
for each of the algorithms in the description box.
Because if you want more in-depth understanding
of each of the algorithms,
you can check out that content.
Since this is a full course video,
I have to cover all the topics,
and it is hard for me to make you understand
in-depth of each topic.
So I'll leave a couple of links in the description box.
You can watch those videos as well.
Make sure you checkout the probability
and statistics video.
So now let's move on and locate our next algorithm,
which is the K nearest neighbor algorithm.
Now KNN, which basically stands for K nearest neighbor,
is, again, a supervised classification algorithm
that classifies a new data point into the target class
or the output class, depending on the features
of its neighboring data points.
That's why it's called K nearest neighbor.
So let's try to understand KNN with a small analogy.
Okay, let's say that we want a machine
to distinguish between the images of cats and dogs.
So to do this, we must input our data set
of cat and dog images,
and we have to train our model to detect the animal
based on certain features.
For example, features such as pointy ears
can be used to identify cats.
Similarly, we can identify dogs
based on their long ears.
So after starting the data set
during the training phase,
when a new image is given to the model,
the KNN algorithm will classify it
into either cats or dogs,
depending on the similarity in their features.
Okay, let's say that a new image has pointy ears,
it will classify that image as cat,
because it is similar to the cat images,
because it's similar to its neighbors.
In this manner, the KNN algorithm classifies
the data point based on how similar they are
to their neighboring data points.
So this is a small example.
We'll discuss more about it in the further slides.
Now let me tell you a couple of
features of KNN algorithm.
So, first of all, we know that
it is a supervised learning algorithm.
It uses labeled input data set
to predict the output of the data points.
Then it is also one of the simplest
machine learning algorithms,
and it can be easily implemented
for a varied set of problems.
Another feature is that it is non-parametric,
meaning that it does not take in any assumptions.
For example, naive Bayes is a parametric model,
because it assumes that all the independent variables
are in no way related to each other.
It has assumptions about the model.
K nearest neighbor has no such assumptions.
That's why it's considered a non-parametric model.
Another feature is that it is a lazy algorithm.
Now, lazy algorithm basically is any algorithm
that memorizes the training set,
instead of learning a discriminative function
from the training data.
Now, even though KNN is mainly a classification algorithm,
it can also be used for regression cases.
So KNN is actually both a classification
and a regression algorithm.
But mostly, you'll see that it'll be used
on the four classification problems.
The most important feature about
a K nearest neighbor is that
it's based on feature similarity
with its neighboring data points.
You'll understand this
in the example that I'm gonna tell you.
Now, in this image, we have two classes of data.
We have class A which is squares
and class B which are triangles.
Now the problem statement is to assign
the new input data point
to one of the two classes
by using the KNN algorithm.
So the first step in the KNN algorithm
is to define the value of K.
But what is the K in the KNN algorithm stand for?
Now the K stands for the number of nearest neighbors,
and that's why it's got the name K nearest neighbors.
Now, in this image, I've defined the value of K as three.
This means that the algorithm
will consider the three neighbors
that are closest to the new data point
in order to decide the class of the new data point.
So the closest between the data point
is calculated by using measure
such as Euclidean distance and Manhattan distance,
which I'll be explaining in a while.
So our K is equal to three.
The neighbors include two squares and one triangle.
So, if I were to classify the new data point
based on K equal to three,
then it should be assigned to class A, correct?
It should be assigned to squares.
But what if the K value is set to seven.
Here I'm basically telling my algorithm
to look for the seven nearest neighbors
and classify the new data point
into the class it is most similar to.
So our K equal to seven.
The neighbors include three squares and four triangles.
So if I were to classify the new data point
based on K equal to seven,
then it would be assigned to class B,
since majority of its neighbors are from class B.
Now this is where a lot of us get confused.
So how do we know which K values is the most suitable
for K nearest neighbor.
Now there are a couple methods
used to calculate the K value.
One of them is known as the elbow method.
We'll be discussing the elbow method
in the upcoming slides.
So for now let me just show you
the measures that are involved behind KNN.
Okay, there's very simple math
behind the K nearest neighbor algorithm.
So I'll be discussing the Euclidean distance with you.
Now in this figure, we have to measure the distance
between P one and P two by using Euclidean distance.
I'm sure a lot of you
already know what Euclidean distance is.
It is something that we learned in eighth or 10th grade.
I'm not sure.
So all you're doing is you're extracting X one.
So the formula is basically x two minus x one
the whole square
plus y two minus y one the whole square,
and the root of that is the Euclidean distance.
It's as simple as that.
So Euclidean distance is used
as a measure to check the closeness of data points.
So basically, KNN uses the Euclidean distance
to check the closeness of a new data point
with its neighbors.
So guys, it's as simple as that.
KNN makes use of simple measures
in order to solve very complex problems.
Okay, and this is one of the reasons why
KNN is such a commonly used algorithm.
Coming to support vector machine.
Now, this is our last algorithm
under classification algorithms.
Now guys, don't get paranoid because of the name.
Support vector machine actually
is one of the simplest algorithms in supervised learning.
Okay, it is basically used to classify data
into different classes.
It's a classification algorithm.
Now unlike most algorithms,
SVM makes use of something known as a hyperplane
which acts like a decision boundary
between the separate classes.
Okay.
Now SVM can be used to generate multiple
separating hyperplane,
such that the data is divided into segments,
and each segment contains only one kind of data.
So, a few features of SVM include that
it is a supervised learning algorithm,
meaning that it's going to study a labeled training data.
Another feature is that it is again
a regression and a classification algorithm.
Even though SVM is mainly used for classification,
there is something known as the support vector regressor.
That is useful regression problems.
Now, SVM can also be used to classify non-linear data
by using kernel tricks.
Non-linear data is basically data
that cannot be separated
by using a single linear line.
I'll be talking more about this
in the upcoming slides.
Now let's move on and discuss how SVM works.
Now again, in order to make you understand
how support vector machine works,
you look at a small scenario.
For a second, pretend that you own a farm
and you have a problem.
You need to set up a fence
to protect your rabbits from a pack of wolves.
Okay, now, you need to decide
where you want to build your fence.
So one way to solve the problem is by using
support vector machines.
So if I do that and if I try to draw a decision boundary
between the rabbits and the wolves,
it looks something like this.
Now you can clearly build a fence along this line.
So in simple terms, this is exactly how
your support vector machines work.
It draws a decision boundary,
which is nothing but a hyperplane
between any two classes in order to separate them
or classify them.
Now I know that you're thinking how do you know
where to draw a hyperplane.
The basic principle behind SVM
is to draw a hyperplane
that best separates the two classes.
In our case, the two classes
are the rabbits and the wolves.
Now before we move any further,
let's discuss the different terminologies
that are there in support vector machine.
So that is basically a hyperplane.
It is a decision boundary that best separates
the two classes.
Now, support vectors, what exactly are support vectors.
So when you start with the support vector machine,
you start by drawing a random hyperplane.
And then you check the distance
between the hyperplane and the closest data point
from each of the class.
These closest data points to the hyperplane
are known as support vectors.
Now these two data points
are the closest to your hyperplane.
So these are known as support vectors,
and that's where the name comes from,
support vector machines.
Now the hyperplane is drawn
based on these support vectors.
And optimum hyperplane will be
the one which has a maximum distance
from each of the support vectors,
meaning that the distance between the hyperplane
and the support vectors has to be maximum.
So, to sum it up, SVM is used to classify data
by using a hyperplane,
such that the distance between the hyperplane
and the support vector is maximum.
Now this distance is nothing but the margin.
Now let's try to solve a problem.
Let's say that I input a new data point
and I want to draw a hyperplane
such that it best separates these two classes.
So what do I do?
I start out by drawing a hyperplane,
and then I check the distance between the hyperplane
and the support vectors.
So, basically here, I'm trying to check
if the margin is maximum for this hyperplane.
But what if I drew the hyperplane like this?
The margin for this hyperplane is clearly being more
than the previous one.
So this is my optimal hyperplane.
This is exactly how you understand
which hyperplane needs to be chosen,
because you can draw multiple hyperplanes.
Now, the best hyperplane is the one
that has a maximum module.
So, this is my optimal hyperplane.
Now so far it was quite easy.
Our data was linearly separable,
which means that you could draw a straight line
to separate the two classes.
But what will you do if the data looks like this?
You possibly cannot draw a hyperplane like this.
It doesn't separate the two classes.
We can clearly see rabbits and wolves
in both of the classes.
Now this is exactly where non-linear SVM
comes into the picture.
Okay, this is what the kernel trick is all about.
Now, kernel is basically something that can be used
to transform data into another dimension
that has a clear dividing margin between classes of data.
So, basically the kernel function
offers the user the option of transforming
non-linear spaces into linear ones.
Until this point, if you notice that
we were plotting our data on two dimensional space.
We had x and y-axis.
A simple trick is transforming the two variables,
x and y, into a new feature space,
which involves a new variable z.
So, basically, what we're doing
is we're visualizing the data
on a three dimensional space.
So when you transform the 2D space into a 3D space,
you can clearly see a dividing margin
between the two classes of data.
You can clearly draw a line in the middle
that separates these two data sets.
So guys, this sums up the whole idea behind
support vector machines.
Support vector machines are very easy to understand.
Now, this was all for our
supervised learning algorithms.
Now, before I move on to unsupervised learning algorithms,
I'll be running a demo.
We'll be running a demo
in order to understand all the classification algorithms
that we studied so far.
Earlier in the session, we ran a demo
for the regression algorithms.
Now we'll run for the classification algorithms.
So, enough of theory.
Let's open up Python,
and let's start looking at how
these classification algorithms work.
Now, here what we'll be doing
is we'll implement multiple classification algorithms
by using the scikit-learn.
Okay, it's one of the most popular
machine learning tool for Python.
Now we'll be using a simple data set
for the task of training a classifier to distinguish
between the different types of fruits.
The purpose of this demo is to implement
multiple classification algorithms
for the same set of problem.
So as usual, you start by importing
all your libraries in Python.
Again, guys, if you don't know Python,
check the description box,
I'll leave a link there.
You can go through that video as well.
Next, what we're doing is we're reading the fruit data
in the form of table.
You stored it in a variable called fruits.
Now if you wanna see the first few rows of the data,
let's print the first few observations in our data set.
So, this is our data set.
These are the fruit labels.
So we have around four fruits in our data set.
We have apple, we have mandarin,
orange, and lemon.
Okay.
Now, fruit label denotes nothing but the label
of apple, which is one.
Mandarin has two.
Similarly, orange is labeled as three.
And lemon is labeled as four.
Then a fruit subtype is basically
the family of fruit it belongs to.
Mass is the mass of the fruit,
width, height, and color score.
These are all our predictor variables.
We have to identify the type of fruit,
depending on these predictor variables.
So, first, we saw a couple of observations over here.
Next, if you want to see the shape of your data set,
this is what it looks like.
There are around 59 observations with
seven predictor variables,
which is one, two, three, four, five, six, and seven.
We have seven variables in total.
Sorry, not predictor variables.
This seven denotes both your predictor
and your target variable.
Next, I'm just showing you the four fruits that we have
in our data set,
which is apple, mandarin, orange, and lemon.
Next, I'm just grouping fruits by their names.
Okay.
So we have 19 apples in our data set.
We have 16 lemons.
We have only five mandarins,
and we have 19 oranges.
Even though the number of mandarin samples is low,
we'll have to work with it,
because right now I'm just trying to make you
understand the classification algorithms.
The main aim for me behind doing these demos
is so that you understand
how classification algorithms work.
Now what you can do is you can also plot a graph
in order to see the frequency of each of these fruits.
Okay, I'll show you what the plot looks like.
The number of apples and oranges is the same.
We have I think around 19 apples and oranges.
And similarly, this is the count for lemons.
Okay.
So this is a small visualization.
Guys, visualization is actually very important
when it comes to machine learning,
because you can see most of the relations
and correlations by plotting graphs.
You can't see those correlations
by just running code and all of that.
Only when you plot different variables on your graph,
you'll understand how they are related.
One of the main task in machine learning
is to visualize data.
It ensures that you understand
the correlation between data.
Next, what we're gonna do is we'll graph
something known as a box plot.
Okay, a box plot basically helps you understand
the distribution of your data.
Let me run the box plot,
and I'll show you what exactly I mean.
So this is our box plot.
So, box plot will basically give you
a clearer idea of the distribution
of your input variables.
It is mainly used in exploratory data analysis,
and it represents the distribution of the data
and its variability.
Now, the box plot contains
upper quartile and lower quartile.
So the box plot basically spanned your interquartile range
or something known as IQR.
IQR is nothing but your third quartile
subtracted from your first quartile.
Now again, this involves statistics and probability.
So I'll be leaving a link in the description box.
You can go through that video.
I've explained statistics probability, IQR,
range, and all of that in there.
So, one of the main reasons why box plots are used
is to detect any sort of outliers in the data.
Since the box plot spans the IQR,
it detects the data point
that lie outside the average range.
So if you see in the colored space,
most of the data is distributed around the IQR,
whereas here the data are not that well distributed.
Height also is not very well distributed,
but color space is pretty well distributed.
This is what the box plot shows you.
So guys, this involves a lot of math.
ALl of these, each and every function in machine learning
involves a lot of math.
So you know it's necessary to have a good understanding
of statistics, probability, and all of that.
Now, next, what we'll do is we'll plot a histogram.
Histogram will basically show you
the frequency of occurrence.
Let me just plot this, and then we'll try and understand.
So here you can understand a few correlations.
Okay, some pairs of these attributes are correlated.
For example, mass and width,
they're somehow correlated along the same ranges.
So this suggests a high correlation
and a predictable relationship.
Like if you look at the graphs, they're quite similar.
So for each of the predictor variables,
I've drawn a histogram.
For each of that input data, we've drawn a histogram.
Now guys, again, like i said,
plotting graphs is very important
because you understand a lot of correlations
that you cannot understand
by just looking at your data,
or just running operations on your data.
Repeat, or just running code on your data.
Okay.
Now, next, what we're doing here is we're just
dividing the data set into target and predictor variables.
So, basically, I've created an array of feature names
which has your predictor variables.
It has mass, width, height, color space.
And you have assigned that as X,
since this is your input,
and y is your output which is your fruit label.
That'll show whether it is an apple,
orange, lemon, and so on.
Now, the next step that we'll perform over here
is pretty evident.
Again, this is data splicing.
So data splicing, by now,
I'm sure all of you know what it is.
It is splitting your data into training and testing data.
So that's what we've done over here.
Next, we're importing something known as the MinMaxScaler.
Scaling or normalizing your data
is very important in machine learning.
Now, I'm seeing this because your raw data
can be very biased.
So it's very important to normalize your data.
Now when I say normalize your data,
so if you look at the value of mass
and if you look at the value of height and color,
you see that mass is ranging in hundreds and double digits,
whereas height is in single digit,
and color score is not even in single digits.
So, if some of your variables have a very high range,
you know they have a very high scale,
like they're in two digits or three digits,
whereas other variables are single digits and lesser,
then your output is going to be very biased.
It's obvious that it's gonna be very biased.
That's why you have to scale your data
in such a way that all of these values
will have a similar range.
So that's exactly what the scaler function does.
Okay.
Now since we have already divided our data
into training and testing data,
our next step is to build the model.
So, first, we're gonna be using
the logistic regression algorithm.
I've already discussed logistic regression with you all.
It's a classification algorithm,
which is basically used to predict the outcome
of a categorical variable.
So we already have the logistic regression class in Python.
All you have to do is you have to
give an instance for this function,
which is logreg over here.
And I'm fitting this instance with a training data set,
meaning that I'm running the algorithm
with the training data set.
Once you do that, you can calculate
the accuracy by using this function.
So here I'm calculate the accuracy
on the training data set
and on the testing data set.
Okay, so let's look at the output of this.
Now guys, ignore this future warning.
Warnings are ignored in Python.
Now, accuracy of the logistic regression classifier
on the training data set is around 70%.
It was pretty good on the training data set.
But when it comes to classifying on the test data set,
it's only 40%,
which is not that good for a classifier.
Now again, this can depend on the problem statement,
for which problem statement
is logistic regression more suitable.
Next, we'll do the same thing using the decision tree.
So again, we just call the decision tree function,
and we'll fit it with the training data set,
and we'll calculate the accuracy
of the decision tree on the training,
and the testing data set.
So if you do that for a decision tree
on the training data set,
you get 100% accuracy.
But on the testing data set,
you have around 87% of accuracy.
This is something that I discussed with you all earlier,
that this is decision trees are very good
with training data set,
because of a process known as overfitting.
But when it comes to classifying
the outcome on the testing data set,
the accuracy reduces.
Now, this is very good compared to logistic regression.
For this problem statement, decision trees
works better that logistic regression.
Coming to KNN classifier.
Again, all you have to do is you have to
call the K neighbor classifier, this function.
And you have to fit this with the training data set.
If you calculate the accuracy for a KNN classifier,
we get a good accuracy actually.
On the training data set,
we get an accuracy of 95%.
And on the testing data set, it's 100%.
That is really good, because our testing data set
actually achieved more of an accuracy
than on a training data set.
Now all of this depends on the value of K
that you've chosen for KNN.
Now, I mentioned that you use the elbow method
to choose the K value in the K nearest neighbor.
I'll be discussing the elbow method in the next section.
So, don't worry if you haven't understood that yet.
Now, we're also using a naive Bayes classifier.
Here we're using a Gaussian naive Bayes classifier.
Gaussian is basically a type of naive Bayes classifier.
I'm not going to go into depth of this,
because it'll just extend our session too much more longer.
Okay.
And if you want to know more about this,
I'll leave a link in the description box.
You can read all about the caution naive Bayes classifier.
Now, the math behind this is the same.
It uses naive Bayes, it uses the Bayes Theorem itself.
Now again, we're gonna call this class,
and then we're going to run our data,
training data on it.
So using the naive Bayes classifier,
we're getting an accuracy of 0.86
on the training data set.
And on the testing data set, we're getting 67% accuracy.
Okay.
Now let's do the same thing with support vector machines.
Importing the support vector classifier.
And we are fitting the training data into the algorithm.
We're getting an accuracy of around 61%
on the training data set and 33% on the testing data set.
Now guys, this accuracy and all
depends also on the problem statement.
It depends on the type of data
that support vector machines get.
Usually, SVM is very good on large data sets.
Now since we have a very small data set over here,
it's sort of obvious by the accuracy, so less.
So guys, these were a couple of classification algorithms
that I showed you here.
Now, because our KNN classifier
classified our data set more accurately
we'll look at the predictions that the KNN classifier mean.
Okay
Now we're storing all our predicted values
in the predict variable.
now in order to show you the accuracy
of the KNN model,
we're going to us something known as the confusion matrix.
So, a confusion matrix is a table
that is often used to describe
the performance of a classification model.
So, confusion matrix actually
represents a tabular representation
of actual versus predicted values.
So when you draw a confusion matrix
on the actual versus predicted values
for the KNN classifier,
this is what the confusion matrix looks like.
Now, we have four rows over here.
If you see, we have four rows.
The first row represents apples,
second, mandarin, third represents lemons,
and fourth, oranges.
So this four value corresponds to zero comma zero,
meaning that it was correctly able to classify
all the four apples.
Okay.
This one value represents one comma one,
meaning that our classifier correctly classified
this as mandarins.
This matrix is drawn on actual values
versus predicted values.
Now, if you look at the summary of the confusion matrix,
we'll get something known as precision recall,
f1-score and support.
Precision is basically the ratio
of the correctly predicted positive observations
to the total predicted positive observations.
So the correctly predicted positive observations are four,
and there are total of four apples
in the testing data set.
So that's where I get a precision of one.
Okay.
Recall on the other hand
is the ratio of correctly predicted positive observations
to all the observations in the class.
Again, we've correctly classified four apples,
and there are a total of four apples.
F1-score is nothing but the weighted average
of your precision and your recall.
Okay, and your support basically denotes
the number of data points
that were correctly classified.
So, in our KNN algorithm, since we got 100% accuracy,
all our data points were correctly classified.
So, 15 out of 15 were correctly classified
because we have 100% accuracy.
So that's how you read a confusion matrix.
Okay, you have four important measures,
precision, recall, f1-score, and support.
F1-score is just the ratio or the weighted average
of your precision and your recall.
So precision is basically the correctly predicted
positive observations to the total predicted
positive observations.
Recall is a ratio of the predicted
positive observations to all your observations.
So guys, that was it for the demo
of classification algorithms,
we discuss regression algorithms
and we discussed classification algorithms.
Now it's time to talk about unsupervised
learning algorithms.
Under unsupervised learning algorithms
may try to solve clustering problems.
And the most important clustering algorithm there is,
known as K-means clustering.
So we're going to discuss the K-means algorithm,
and also show you a demo where we'll be executing
the clustering algorithm,
and you're seeing how it implemented to solve a problem.
Now, the main aim of the K-means algorithm
is to group similar elements or data points in to a cluster.
So it is basically the process by which
objects are classified
interest a predefined number of groups,
so that they are much dissimilar as possible
from one group to another group,
but as much similar as possible within each group.
Now what I mean is let's say you're trying to cluster
this population into four different groups,
such that each group has people within
a specified range of age.
Let's say group one is of people between the age 18 and 22.
Similarly, group two is between 23 and 35.
Group three is 36 and 39 or something like that.
So let's say you're trying to cluster
people into different groups based on their age.
So for such problems, you can make use
of the K-means clustering algorithm.
One of the major applications of the clustering algorithm
is seen in targeted marketing.
I don't know how many of you are aware
of targeted marketing.
Targeted marketing is all about marketing a specific product
to a specific audience.
Let's say you're trying to sell fancy clothes
or a fancy set of bags and all of that.
And the perfect audience for such product
would be teenagers.
It would be people around the age of 16 to 21 or 18.
So that is what target marketing is all about.
Your product is marketed to a specific audience
that might be interested in it.
That is what targeted marketing is.
So K means clustering is use majorly in targeted marketing.
A lot of eCommerce websites like Amazon, Flipkart, eBay.
All of these make use of clustering algorithms
in order to target the right audience.
Now let's see how the K-means clustering works.
Now the K in K-means denotes the number of clusters.
Let's say I give you a data set containing 20 points,
and you want to cluster this data set into four clusters.
That means your K will be equal to four.
So K basically stands for the number of clusters
in your data set,
or the number of clusters you want to form.
You start by defining the number K.
Now for each of these clusters,
you're going to choose a centroid.
So for every cluster,
there are four cluster in our data set.
For each of these clusters,
you'll randomly select one of the data points
as a centroid.
Now what you'll do is you'll start
computing the distance from that centroid
to every other point in that cluster.
As you keep computing the centroid
and the distance between the centroid
and other data points in that cluster,
your centroid keep shifting,
because you're trying to get to the average of that cluster.
Whenever you're trying to get to the average of the cluster,
the centroid keeps shifting,
because the centroid keeps converging and it keeps shifting.
Let's try to understand how K-means works.
Let's say that this data set, this is given to us.
Let's say if you're given random points like these
and you're asked to us K-means algorithm on this.
So your first step will be
to decide the number of clusters you want to create.
So let's say I wanna create three different clusters.
So my K value will be equal to three.
The next step will be to provide
centroids of all the clusters.
What you'll do is initially you'll randomly pick
three data points as your centroids
for your three different clusters.
So basically, this red denotes the centroid for one cluster.
Blue denotes a centroid for another cluster.
And this green dot denotes the centroid
for another cluster.
Now what happens in K-means,
the algorithm will calculate
the Euclidean distance of the points from each centroid
and assign the points to the closest cluster.
Now since we had three centroids here,
now what you're gonna do is
you're going to calculate the distance
from each and every data point
to all the centroids,
and you're going to check which data point
is closest to which centroid.
So let's say your data point A
is closest to the blue centroid.
So you're going to assign the data point A
to the blue cluster.
So based on the distance
between the centroid and the cluster,
you're going to form three different clusters.
Now again, you're going to calculate the centroid
and you're going to form a new cluster
which is from better clusters,
because you're recomputing all those centroids.
Basically, your centroids represent
the mean of each of your cluster.
So you need to make sure
that your mean is actually the centroid of each cluster.
So you'll keep recomputing this centroids
until the position of your centroid does not change.
That means that your centroid is actually the main
or the average of that particular cluster.
So that's how K-means works.
It's very simple.
All you have to do is you have to start
by defining the K value.
After that, you have to randomly
pick the number of case centroids.
Then you're going to calculate the average distance
of each of the data points from the centroids,
and you're going to assign a data point
to the centroid it is closest to.
That's how K-means works.
It's a very simple process.
All you have to do is us have to keep iterating,
and you have to recompute the centroid value
until the centroid value does not change,
until you get a constant centroid value.
Now guys, again, in K-means,
you make use of distance measures like Euclidean.
I've already discussed what Euclidean is all about.
So, to summarize how K-means works,
you start by picking the number of clusters.
Then you pick a centroid.
After that, you calculate the distance
of the objects to the centroid.
Then you group the data points into specific clusters
based on their distance.
You have to keep computing the centroid
until each data point is assigned to the closest cluster,
so that's how K-means works.
Now let's look at the elbow method.
The elbow method is basically used in order to find out
the most optimum k value for a particular problem.
So the elbow method is quite simple actually.
You start off by computing the sum of squared errors
for some values of K.
Now sum of squared error is basically
the sum of the squared distance
between each member of the cluster and its centroid.
So you basically calculate the sum of squared errors
for different values of K.
For example, you can consider K value
as two, four, six, eight, 10, 12.
Consider all these values,
compute the sum of squared errors for each of these values.
Now if you plot your K value
against your sum of squared errors,
you will see that the error decreases as K gets larger.
This is because the number of clusters increase.
If the number of clusters increases,
it means that the distortion gets smaller.
The distortion keeps decreasing
as the number of clusters increase.
That's because the more clusters you have,
the closer each centroid will be with its data points.
So as you keep increasing the number of clusters,
your distortion will also decrease.
So the idea of the elbow method is to choose the K
at which the distortion decreases abruptly.
So if you look at this graph at K equal to four,
the distortion is abruptly decreasing.
So this is how you find the value of K.
When your distortion drops abruptly,
that is the most optimal K value
you should be choosing for your problem statement.
So let me repeat the idea behind the elbow method.
You're just going to graph the number of clusters you have
versus the squared sum of errors.
This graph will basically give you the distortion.
Now the distortion obviously going to decrease
if you increase the number of clusters,
and there is gonna be one point in this graph
wherein the distortion decreases very abruptly.
Now for that point, you need to find out the value of K,
and that'll be your most optimal K value.
That's how you choose your K-means K value
and your KNN K value as well.
So guys, this is how the elbow method is.
It's very simple and it can be easily implemented.
Now we're gonna look at a small demo
which involves K-means.
This is actually a very interesting demo.
Now guys, one interesting application
of clustering is in color compression with images.
For example, imagine you have an image
with millions of colors in it.
In most images, a large number of colors will be unused,
and many of the pixels in the image
will have similar or even identical colors.
Now having too many colors in your image
makes it very hard for image processing an image analysis.
So this is one area where K-means is applied very often.
It's applied in image segmentation, image analysis,
image compression, and so on.
So what we're gonna do in this demo
is we are going to use an image
from the scikit-learn data set.
Okay, it is a prebuilt image,
and you will require to install the pillow package for this.
We're going to use an image
form the scikit-learn data set module.
So we'll begin by importing the libraries as usual,
and we'll be loading our image as china.
The image is china.jpg,
and we'll be loading this in a variable called china.
So if you wanna look at the shape of our image,
you can run this command.
So we're gonna get a three-dimensional value.
So we're getting 427 comma 640 comma three.
Now this is basically a three dimensional array
of size, height, width, and RGB.
It contains red, blue, green contributions,
as integers from zero to 255.
So, your pixel values range between zero and 255,
and I think zero stands for your black,
and 255 represents white if I'm not wrong.
And basically, that's what this array shape denotes.
Now one way we can view this set of pixels
is as a cloud of points in a three dimensional color space.
So what we'll do is we will reshape the data
and rescale the color,
so that they lie between zero and one.
So the output of this will be a two dimensional array now.
So basically, we can visualize these pixels
in this color space.
Now what we're gonna do is we're gonna try
and plot our pixels.
We have a really huge data set
which contains around 16 million possible colors.
So this denotes a very, very large data set.
So, let me show you what it looks like.
We have red against green and red against blue.
These are our RGB value,
and we can have around 16 million possible
combination of colors.
The data set is way too large or us to compute.
So what we'll do is we will reduce these 16 million colors
to just 16 colors.
We can do that by using K-means clustering,
because we can cluster similar colors into similar groups.
So this is exactly where we'll be importing K-means.
Now, one thing to note here is
because we're dealing with a very large data set,
we will use the MinibatchKMeans.
This operates on subsets of the data
to compute the results more quickly and more accurately,
just like the K-means algorithm,
because I told you this data set is really huge.
Even though this is a single image,
the number of pixel combinations can come up to 16 million,
which is a lot.
Now each pixel is considered as a data point
when you've taken image into consideration.
When you have data points and data values,
that's different.
When you're starting an image for image classification
or image segmentation,
each and every pixel is considered.
So, basically, you're building matrices
of all of these pixel values.
So having 16 million pixels is a very huge data set.
So, for that reason, we'll be using the MinibatchKMeans.
It's very similar to K-means.
The only difference is that it'll operate
on subsets of the data.
Because the data set is too huge, it'll operate on subsets.
So, basically, we're making use of K-means
in order to cluster these 16 million
color combinations into just 16 colors.
So basically, we're gonna form 16 clusters
in this data set.
Now, the result is the recoloring of the original pixel
where every pixel is assigned the color
of its closest cluster center.
Let's say that there are a couple of colors
which are very close to green.
So we're going to cluster all of these similar colors
into one cluster.
We'll keep doing this until we get 16 clusters.
So, obviously, to do this, we'll be using
the clustering method, K-means.
Let me show you what the output looks like.
So, basically, this was the original image
from the scikit data set,
and this is the 16-color segmented image.
Basically, we have only 16 colors here.
Here we can have around 16 million colors.
Here there are only 16 colors.
If you can't also, you can only see particular colors.
Now obviously there's a lot of distortion over here,
but this is how you study an image.
Remove all the extra contrast that is there in an image.
You try to reduce the pixel
to a smaller set of data as possible.
The more varied pixels you have,
the harder it is going to be for you
to study the image for analysis.
Now, obviously, there are some details
which are lost in this.
But overall, the image is still recognizable.
So here, basically, we've compressed this
with a compression factor of around one million,
because each cluster will have around
one million data points in it,
or pixel values in it, or pixels in it.
Now this is an interesting application of K-means.
There are actually better ways
you can compress information on image.
So, basically, I showed you this example
because I want you to understand
the power of K-means algorithm.
You can cluster a data set that is this huge
into just 16 colors.
Initially, there were 16 million,
and now you can cluster it to 16 colors.
So guys, K-means plays a very huge role
in computer vision image processing,
object detection, and so on.
It's a very important algorithm
when it comes to detecting objects.
So in self-driving cars and all
can make use of such algorithms.
So guys, that was all about unsupervised learning
and supervised learning.
Now it's the last type of machine learning,
which is reinforcement learning.
Now this is actually
a very interesting part of machine learning,
and it is quite difference from supervised and unsupervised.
So we'll be discussing all the concepts
that are involved in reinforcement learning.
And also reinforcement learning
is a little more advanced.
When I say advanced, I mean that it's been used
in applications such as self-driving cars
and is also a part of
a lot of deep learning applications,
such as AlphaGo and so on.
So, reinforcement learning
has a different concept to it itself.
So we'll be discussing all the concepts under it.
So just to brush up your information
about reinforcement learning,
reinforcement learning is a part of machine learning
where an agent is put in an unknown environment,
and he learns how to behave in this environment
by performing certain actions and observing the rewards
which it gets from these actions.
Reinforcement learning is all about taking
an appropriate action in order to maximize the reward
in a particular situation.
Now let's understand reinforcement learning
with an analogy.
Let's consider a scenario
wherein a baby is learning how to walk.
This scenario can go about in two different ways.
The first is baby starts walking
and it makes it to the candy.
And since the candy is the end goal,
the baby is very happy and it's positive.
Meaning, the baby is happy
and it received a positive reward.
Now, the second way this can go in
is that the baby starts walking,
but it falls due to some hurdle between.
That's really cute.
So the baby gets hurt and it doesn't get to the candy.
It's negative because the baby is sad
and it receives a negative reward.
So just like how we humans learn from our mistakes
by trial and error,
reinforcement learning is also similar.
Here we have an agent,
and in this case, the agent is the baby,
and the reward is the candy
with many hurdles in between.
The agent is supposed to find
the best possible path to reach the reward.
That is the main goal of reinforcement learning.
Now the reinforcement learning process
has two important components.
It has something known as an agent
and something known as an environment.
Now the environment is
the setting that the agent is acting on,
and the agent represents the
reinforcement learning algorithm.
The whole reinforcement learning is basically the agent.
The environment is the setting
in which you place the agent,
and it is the setting
wherein the agent takes various action.
The reinforcement learning process
starts when the environment sends a state to the agent.
Now the agent, based on the observations it makes,
it takes an action in response to that state.
Now, in turn, the environment will send the next state
and the respective reward back to the agent.
Now the agent will update its knowledge
with the reward returned by the environment
to evaluate its last actions.
The loop continues until the environment
sends a terminal state
which means that the agent has accomplished
all of its task.
To understand this better,
let's suppose that our agent is playing Counter Strike.
The reinforcement learning process
can be broken down into a couple of steps.
The first step is the reinforcement learning agent,
which is basically the player,
he collects a state, S naught, from the environment.
So whenever you're playing Counter Strike,
you start off with stage zero or stage one.
You start off from the first level.
Now based on this state, S naught,
the reinforcement learning agent
will take an action, A naught.
So guys, action can be anything that causes a result.
Now if the agent moves left or right in the game,
that is also considered as an action.
So initially, the action will be random,
because the agent has no clue about the environment.
Let's suppose that you're playing Counter Strike
for the first time.
You have no idea about how to play it,
so you'll just start randomly.
You'll just go with whatever,
whichever action you think is right.
Now the environment is now in a stage one.
After passing stage zero,
the environment will go into stage one.
Once the environment updates the stage to stage on,
the reinforcement learning agent
will get a reward R one from the environment.
This reward can be anything like additional points
or you'll get additional weapons
when you're playing Counter Strike.
Now this reinforcement learning loop will go on
until the agent is dead or reaches the destination,
and it continuously outputs
a sequence of state action and rewards.
This exactly how reinforcement learning works.
It starts with the agent being put in an environment,
and the agent will randomly take
some action in state zero.
After taking an action, depending on his action,
he'll either get a reward
and move on to state number one,
or he will either die and go back to the same state.
So this will keep happening
until the agent reaches the last stage,
or he dies or reaches his destination.
That's exactly how reinforcement learning works.
Now reinforcement learning is the logic
behind a lot of games these days.
It's being implemented in various games, such as Dota.
A lot of you who play Dota might know this.
Now let's talk about a couple of
reinforcement learning definitions or terminologies.
So, first, we have something known as the agent.
Like I mentioned, an agent
is the reinforcement learning algorithm
that learns from trial and error.
An agent is the one that takes actions like,
for example, a solider in Counter Strike
navigating through the game,
going right, left, and all of that.
Is the agent taking some action?
The environment is because the world
through which the agent moves.
Now the environment, basically,
takes the agent's current state and action as input,
and returns the agent's reward
and its next state as the output.
Next, we have something known as action.
All the possible steps that an agent can take
is considered as an action.
Next, we have something known as state.
Now the current condition returned by the environment
is known as a state.
Reward is an instant return from the environment
to apprise the last action
of the reinforcement learning agent.
All of these terms are pretty understandable.
Next, we have something known as policy.
Now, policy is the approach that the agent uses
to determine the next action
based on the current state.
Policy is basically the approach
with which you go around in the environment.
Next, we have something known as value.
Now, the expected long-term return with a discount,
as opposed to the short-term rewards R,
is known as value.
Now, terms like discount and value,
I'll be discussing in the upcoming slides.
Action-value is also very similar to the value,
except it takes an extra parameter
known as the current action.
Don't worry about action and Q value.
We'll talk about all of this in the upcoming slides.
So make yourself familiar with these terms,
because we'll be seeing a whole lot of them this session.
So, before we move any further,
let's discuss a couple of more
reinforcement learning concepts.
Now we have something known as the reward maximization.
So if you haven't realized it already,
the basic aim of reinforcement learning agent
is to maximize the report.
How does this happen?
Let's try to understand this in a little more detail.
So, basically the agent works based on the theory
of reward maximization.
Now that's exactly why the agent must be trained
in such a way that he takes the best action,
so that the reward is maximal.
Now let me explain a reward maximization
with a small example.
Now in this figure, you can see there is a fox,
there is some meat, and there is a tiger.
Our reinforcement learning agent is the fox.
His end goal is to eat the maximum amount of meat
before being eaten by the tiger.
Now because the fox is a very clever guy,
he eats the meat that is closer to him,
rather than the meat which is close to the tiger,
because the closer he gets to the tiger,
the higher are his chances of getting killed.
That's pretty obvious.
Even if the reward near the tiger are bigger meat chunks,
that'll be discounted.
This is exactly what discount is.
We just discussed it in the previous slide.
This is done because of the uncertainty factor
that the tiger might actually kill the fox.
Now the next thing to understand is how discounting
of a reward works.
Now, in order to understand discounting,
we define a discount rate called gamma.
The value of gamma is between zero and one.
And the smaller the gamma,
the larger the discount and so on.
Now don't worry about these concepts,
gamma and all of that.
We'll be seeing that in our practical demo today.
So let's move on and discuss another concept
known as exploration and exploitation trade-off.
Now guys, before that, I hope all of you understood
reward maximization.
Basically, the main aim behind reinforcement learning
is to maximize the rewards that an agent can get.
Now, one of the most important concepts
in reinforcement learning is
the exploration and exploitation trade-off.
Now, exploration, like the name suggests,
it's about exploring and capturing
more information about an environment.
On the other hand, exploitation is about
using the already known exploited information
to heighten your reward.
Now consider the same example
that we saw previously.
So here the fox eats only the meat chunks
which are close to him.
He doesn't eat the bigger meat chunks
which are at the top,
even though the bigger meat chunks
would get him more reward.
So if the fox only focuses on the closest reward,
he will never reach the big chunks of meat.
This process is known as exploitation.
But if the fox decide to explore a bit,
it can find the bigger reward,
which is the big chunk of meat.
This is known as exploration.
So this is the difference between exploitation
and exploration.
It's always best if the agent explores the environment,
tries to figure out a way in which we can get
the maximum number of rewards.
Now let's discuss another important concept
in reinforcement learning,
which is known as the Markov's decision process.
Basically, the mathematical approach for mapping
a solution in reinforcement learning
is called Markov's decision process.
It's the mathematics behind reinforcement learning.
Now, in a way, the purpose of reinforcement learning
is to solve a Markov's decision process.
Now in order to get a solution,
there are a set of parameters
in a Markov's decision process.
There's a set of actions A,
there's a set of states S,
a reward R, policy pi, and value V.
Also, this image represents
how a reinforcement learning works.
There's an agent.
The agent take some action on the environment.
The environment, in turn, will reward the agent,
and it will give him the next state.
That's how reinforcement learning works
so to sum everything up,
what happens in Markov's decision process
and reinforcement learning is
the agent has to take an action A
to transition from the start state
to the end state S.
While doing so, the agent will receive some reward R
for each action he takes.
Now the series of action that are taken by the agent
define the policy and the rewards collected
to find the value.
The main goal here is to maximize the rewards
by choosing the optimum policy.
So you're gonna choose the best possible approach
in order to maximize the rewards.
That's the main aim of Markov's decision process.
To understand Markov's decision process,
let's look at a small example.
I'm sure all of you already know
about the shortest path problem.
We all had such problems and concepts in math
to find the shortest path.
Now consider this representation over here, this figure.
Here, our goal is to find the shortest path
between two nodes.
Let's say we're trying to find
the shortest path between node A and node D.
Now each edge, as you can see,
has a number linked with it.
This number denotes the cost to traverse
through that edge.
So we need to choose a policy to travel from A to D
in such a way that our cost is minimum.
So in this problem, the set of states are
denoted by the nodes A, B, C, D.
The action is to traverse from one node to the other.
For example, if you're going from to A C,
there is an action.
C to B is an action.
B to D is another action.
The reward is the cost represented by each edge.
Policy is the path taken to reach the destination.
So we need to make sure that we choose a policy
in such a way that our cost is minimal.
So what you can do is you can start off at node A,
and you can take baby steps to reach your destination.
Initially, only the next possible node is visible to you.
So from A, you can either go to B
or you can go to C.
So if you follow the greedy approach
and take the most optimum step,
which is choosing A to C,
instead of choosing A to B to C.
Now you're at node C
and you want to traverse to node D.
Again, you must choose your path very wisely.
So if you traverse from A to C,
and C to B, and B to D,
your cost is the lest.
But if you traverse from A to C to D,
your cost will actually increase.
Now you need to choose a policy
that will minimize your cost over here.
So let's say, for example, the agent
chose A to C to D.
It came to node C, and then it directly chose D.
Now the policy followed by our agent in this problem
is exploitation type,
because we didn't explore the other notes.
We just selected three nodes and we traversed through them.
And the policy we followed is not actually
an optimal policy.
We must always explore more
to find out the optimal policy.
Even if the other nodes are not giving us any more reward
or is actually increasing our cost,
we still have to explore and find out
if those paths are actually better.
That policy is actually better.
The method that we implemented here
is known as the policy-based learning.
Now the aim here is to find the best policy
among all the possible policies.
So guys, apart from policy-based,
we also have value-based approach
and action-based approach.
Value based emphasizes on maximizing the rewards.
And in action base, we emphasize
on each action taken by the agent.
Now a point to note is that
all of these learning approaches have a simple end goal.
The end goal is to effectively guide the agent
through the environment,
and acquire the most number of rewards.
So this was very simple to understand
Markov's decision process,
exploitation and exploration trade-off,
and we also discussed
the different reinforcement learning definitions.
I hope all of this was understandable.
Now let's move on and understand
an algorithm known as Q-learning algorithm.
So guys, Q-learning is one of the most important algorithms
in reinforcement learning.
And we'll discuss this algorithm
with the help of a small example.
We'll study this example,
and then we'll implement the same example using Python,
and we'll see how it works.
So this is how our demonstration looks for now.
Now the problem statement is to place an agent
in any one of the rooms numbered
zero, one, two, three, and four.
And the goal is for the agent
to reach outside the building,
which is room number five.
So, basically, this zero, one, two, three, four
represents the building,
and five represents a room which is outside the building.
Now all these rooms are connected by those.
Now these gaps that you see between the rooms
are basically those,
and each room is numbered from zero to four.
The outside of the building
can be taught of as a big room
which is room number five.
Now if you've noticed this diagram,
the door number one and door number four
lead directly to room number five.
From one, you can directly go to five,
and from four, also, you can directly go to five.
But if you want to go to five from room number two,
then you'll first have to go to room number three,
room number one, and then room number five.
So these are indirect links.
Direct links are from room number one and room number four.
So I hope all of you are clear with the problem statement.
You're basically going to have
a reinforcement learning agent,
and than agent has to traverse through all the rooms
in such a way that he reaches room number five.
To solve this problem,
first, what we'll do is we'll represent the rooms
on a graph.
Now each room is denoted as anode,
and the links that are connecting these nodes are the doors.
Alright, so we have node one to five,
and the links between each of these nodes
represent the doors.
So, for example, if you look at this graph over here,
you can see that there is a direct connection
from one to five,
meaning that you can directly go from room number one
to your goal, which is room number five.
So if you want to go from room number three to five,
you can either go to room number one,
and then go to five,
or you can go from room number three to four,
and then to five.
So guys, remember, end goal is to reach room number five.
Now to set the room number five as the goal state,
what we'll do is we'll associate a reward value
to each door.
The doors that lead immediately to the goal
will have an instant reward of 100.
So, basically, one to five will have a reward of hundred,
and four to five will also have a reward of hundred.
Now other doors that are not directly
connected to the target room
will have a zero reward,
because they do not directly lead us to that goal.
So let's say you placed the agent in room number three.
So to go from room number three to one,
the agent will get a reward of zero.
And to go from one to five,
the agent will get a reward of hundred.
Now because the doors are two-way,
the two arrows are assigned to each room.
You can see an arrow going towards the room
and one coming from the room.
So each arrow contains an instant reward
as shown in this figure.
Now of course room number five
will loop back to itself with a reward of hundred,
and all other direct connections to the goal room
will carry a reward of hundred.
Now in Q-learning, the goal is to reach the state
with the highest reward.
So that if the agent arrives at the goal,
it will remain there forever.
So I hope all of you are clear with this diagram.
Now, the terminologies in Q-learning
include two terms, state and action.
Okay, your room basically represents the state.
So if you're in state two,
it basically means that you're in room number two.
Now the action is basically the moment of the agent
from one room to the other room.
Let's say you're going from room number two
to room number three.
That is basically an action.
Now let's consider some more example.
Let's say you place the agent in room number two
and he has to get to the goal.
So your initial state will be state number two
or room number two.
Then from room number two, you'll go to room number three,
which is state three.
Then from state three, you can either go back to state two
or go to state one or state four.
If you go to state four, from there you can directly go to
your goal room, which is five.
This is how the agent is going to traverse.
Now in order to depict the rewards that you're going to get,
we're going to create a matrix known as the reward matrix.
Okay, this is represented by R
or also known as the R matrix.
Now the minus one in this table represents null values.
That is basically where there isn't a link
between the nodes that is represented as minus one.
Now there is no link between zero and zero.
That's why it's minus one.
Now if you look at this diagram,
there is no direct link from zero to one.
That's why I've put minus one over here as well.
But if you look at zero comma four,
we have a value of zero over here,
which means that you can traverse from zero to four,
but your reward is going to be zero,
because four is not your goal state.
However, if you look at the matrix,
look at one comma five.
In one comma five, we have a reward value of hundred.
This is because you can directly go
from room number one to five,
and five is the end goal.
That's why we've assigned a reward of hundred.
Similarly, for four comma five,
we have a reward of hundred.
And for five comma five,
we have a reward of hundred.
Zeroes basically represent other links,
but they are zero because they do not lead to the end goal.
So I hope you all understood the reward matrix.
It's very simple.
Now before we move any further,
we'll be creating another matrix
known as the equitable Q matrix.
Now the Q matrix basically represents the memory
of what the agent has learned through experience.
The rules of the Q matrix
will represent the current state of the agent.
The columns will represent the next possible actions
leading to the next state,
and the formula to calculate the Q matrix
is this formula, right?
Here we have Q state comma action,
R state comma action,
which is nothing but the reward matrix.
Then we have a parameter known as the Gamma parameter,
which I'll explain shortly.
And then we are multiplying this with a maximum
of Q next state comma all actions.
Now don't worry if you haven't understood this formula.
I'll explain this with a small example.
For now, let's understand what a Gamma parameter is.
So, basically, the value of Gamma
will be between zero and one.
If Gamma is closer to zero,
it means that the agent will tend to consider
only immediate rewards.
Now, if the Gamma is closer to one,
it means that the agent will consider future rewards
with greater weight.
Now what exactly I'm trying to say is
if Gamma is closer to one,
then we'll be performing something known as exploitation.
I hope you all remember what exploitation
and exploration trade-off is.
So, if your gamma is closer to zero,
it means that the agent
is not going to explore the environment.
Instead, it'll just choose a couple of states,
and it'll just traverse through those states.
But if your gamma parameter is closer to one,
it means that the agent will traverse
through all possible states,
meaning that it'll perform exploration,
not exploitation.
So the closer your gamma parameter is to one,
the more your agent will explore.
This is exactly what Gamma parameter is.
If you want to get the best policy,
it's always practical that you choose a Gamma parameter
which is closer to one.
We want the agent to explore the environment
as much as possible
so that it can get the best policy and the maximum rewards.
I hope this is clear.
Now let me just tell you
what a Q-learning algorithm is step by step.
So you begin the Q-learning algorithm
by setting the Gamma parameter
and the environment rewards in matrix R.
Okay, so, first, you'll have set these two values.
We've already calculated the reward matrix.
We need to set the Gamma parameter.
Next, you'll initialize the matrix Q to zero.
Now why do you do this?
Now, if you remember, I said that
Q matrix is basically the memory of the agent.
Initially, obviously,
the agent has no memory of the environment.
It's new to the environment
and you're placing it randomly anywhere.
So it has zero memory.
That's why you initialize the matrix Q to zero.
After that, you'll select a random initial state,
and you place your agent in that initial state.
Then you'll set this initial state as your current state.
Now from the current state, you'll select some action
that will lead you to the next state.
Then you'll basically get the maximum Q value
for this next state,
based on all the possible actions that we take.
Then you'll keep computing the skew value
until you reach the goals state.
Now that might be a little bit confusing,
so let's look at this entire thing with a small example.
Let's say that first, you're gonna begin
with setting your Gamma parameter.
So I'm setting my Gamma parameter to 0.8
which is pretty close to one.
This means that our agent will explore the environment
as much as possible.
And also, I'm setting the initial state as room one.
Meaning, I'm in state one or I'm in room one.
So basically, your agent is going to be in room number one.
The next step is to initialize the Q matrix as zero matrix.
So this is a Q matrix.
You can see that everything is set to zero,
because the agent has no memory at all.
He hasn't traversed to any node,
so he has no memory.
Now since the agent is in room one
he can either go to room number three
or he can go to room number five.
Let's randomly select room number five.
So, from room number five,
you're going to calculate the maximum Q value
for the next state based on all possible actions.
So all the possible actions from room number five
is one, four, and five.
So, basically, the traversing from Q one comma five,
that's why I put one comma five over here,
state comma action.
Your reward matrix will have R one comma five.
Now R one comma five is basically hundred.
That's why I put hundred over here.
Now your comma parameter is 0.8.
So, guys, what I'm doing here
is I'm just substituting the values in this formula.
So let me just repeat this whole thing.
Q state comma action.
So you're in state number one, correct?
And your action is you're going to room number five.
So your Q state comma action is one comma five.
Again, your reward matrix R one comma five is hundred.
So here's you're gonna put hundred,
plus your Gamma parameter.
Your Gamma parameter is 0.8.
Then you're going to calculate the maximum Q value
for the next state based on all possible actions.
So let's look at the next state.
From room number five, you can go to either one.
You can go to four or you can go to five.
So your actions are five comma one, five comma four,
and five comma five.
That's exactly what I mentioned over here.
Q five comma one, Q five comma four, and Q five comma five.
You're basically putting all the next possible actions
from state number five.
From here, you'll calculate the maximum
Q value that you're getting for each of these.
Now your Q value is zero,
because, initially, your Q matrix is set to zero.
So you're going to get zero for Q five comma one,
five comma four, and five comma five.
So that's why you'll get 0.8 and zero,
and hence your Q one comma five becomes hundred.
This hundred comes from R one comma five.
I hope all of you understood this.
So next, what you'll do is you'll update
this one comma five value in your Q matrix,
because you just calculated Q one comma five.
So I've updated it over here.
Now for the next episode,
we'll start with a randomly chosen initial state.
Again, let's say that we randomly chose state number three.
Now from room number three,
you can either go to room number one, two or four.
Let's randomly select room number one.
Now, from room number five,
you'll calculate the maximum Q value
for the next possible actions.
So let's calculate the Q formula for this.
So your Q state comma action becomes three comma one,
because you're in state number three
and your action is you're going to room number one.
So your R three comma one,
let's see what R three comma one is.
R three comma one is zero.
So you're going to put zero over here,
plus your Gamma parameter, which is 0.8,
and then you're going to check the next possible actions
from room number one,
and you're going to choose the maximum value
from these two.
So Q one comma three and Q one comma five
denote your next possible actions from room number one.
So Q one comma three is zero,
but Q one comma five is hundred.
So we just calculated this hundred in the previous step.
So, out of zero and hundred,
hundred is your maximum value,
so you're going to choose hundred.
Now 0.8 into hundred is nothing but 80.
So again, your Q matrix gets updated.
You see an 80 over here.
So, basically what you're doing is as you're taking actions,
you're updating your Q value,
you're just calculating the Q value at every step,
you're putting it in your Q matrix
so that your agent remembers that,
okay, when I went from room number one to room number five,
I had a Q value of hundred.
Similarly, three to one gave me a Q value of 80.
So basically, this Q matrix represents
the memory of your agent.
I hope all of you are clear with this.
So basically, what we're gonna do
is we're gonna keep iterating through this loop
until we've gone through all possible states
and reach the goal state, which is five.
Also, our main aim here is to find the most optimum policy
to get to room number five.
Now let's implement the exact same thing using Python.
So that was a lot of theory.
Now let's understand how this is done practically.
Alright, so we begin by importing your library.
We're gonna be using the NumPy library over here.
After that, we'll import the R matrix.
We've already created the R matrix.
This is the exact matrix that I showed you
a couple of minutes ago.
So I've created a matrix called R
and I've basically stored all the rewards in it.
If you want to see the R matrix, let me print it.
So, basically, this is your R matrix.
If you remember, node one to five,
you have a reward of hundred.
Node four to five, you have a reward of hundred,
and five to five, you have a reward of hundred,
because all of these nodes directly lead us to the reward.
Correct?
Next, what we're doing is we're creating a Q matrix
which is basically a six into six matrix.
Which represents all the states, zero to five.
And this matrix is basically zero.
After, that we're setting the Gamma parameter.
Now guys, you can play around with this code,
and you know you can change the comma parameter
to 0.7 or 0.9
and see how much more the agent will explore
or whether you perform exploitation.
Here I've set the Gamma parameter 0.8
which is a pretty good number.
Now what I'm doing is I'm setting the initial state as one.
You can randomly choose this state
according to your needs.
I've set the initial state as one.
Now, this function will basically give me
all the available actions from my initial state.
Since I've set my initial state as one,
It'll give me all the possible actions.
Here what I'm doing is since my initial state is one,
I'm checking in my row number one,
which value is equal to zero or greater than zero.
Those denote my available actions.
So look at our row number one.
Here we have one zero and we have a hundred over here.
This is one comma four and this is one comma five.
So if you look at the row number one,
since I've selected the initial state as one,
we'll consider row number one.
Okay, what I'm doing is in row number one,
I have two numbers which are either equal to zero
or greater than zero.
These denote my possible actions.
One comma three has the value of zero
and one comma five has the value of hundred,
which means that the agent
can either go to room number three
or it can go to room number five.
What I'm trying to say is from room number one,
you can basically go to room number three
or room number five.
This is exactly what I've coded over here.
If you remember the reward matrix,
from one you can traverse to only room number three directly
and room number five directly.
Okay, that's exactly what I've mentioned
in my code over here.
So this will basically give me the available actions
from my current state.
Now once I've moved to me next state,
I need to check the available actions from that state.
What I'm doing over here is basically this.
If you're remember,
from room number one, we can go to three and five, correct?
And from three and five,
I'll randomly select the state.
And from that state, I need to find out
all possible actions.
That's exactly what I've done over here.
Okay.
Now this will randomly choose an action for me
from all my available actions.
Next, we need to update our Q matrix,
depending on the actions that we took,
if you remember.
So that's exactly what this update function is four.
Now guys, this entire is for calculating the Q value.
I hope all of you remember the formula,
which is Q state comma action,
R state comma action plus Gamma into max value.
Max value will basically give me the maximum value
out of the all possible actions.
I'm basically computing this formula.
Now this will just update the Q matrix.
Coming to the training phase,
what we're gonna do is we are going to set a range.
Here I've set a range of 10,000,
meaning that my agent will perform 10,000 iterations.
You can set this depending on your own needs,
and 10,000 iteration is a pretty huge number.
So, basically, my agent is going to go through
10,000 possible iterations
in order to find the best policy.
Now this is the exact same thing that we did earlier.
We're setting the current state,
and then we're choosing the available action
from the current state.
The from there, we'll choose an action at random.
Here we'll calculate a Q value
and we'll update the Q value in the matrix.
Alright.
And here I'm doing nothing,
but I'm printing the trained Q matrix.
This was the training phase.
Now the testing phase, basically,
you're going to randomly choose a current state.
You're gonna choose a current state,
and you're going to keep looping
through this entire code,
until you reach the goal state, which is room number five.
That's exactly what I'm doing in this whole thing.
Also, in the end, I'm printing the selected part.
That is basically the policy that the agent took
to reach room number five.
Now if I set the current state as one,
it should give me the best policy
to reach to room number five from room number one.
Alright, let's run this code,
and let's see if it's giving us that.
Now before that happens, I want you to check and tell me
which is the best possible way
to get from room number one to room number five.
It's obviously directly like this.
One to five is the best policy to get from room number one
to room number five.
So we should get an output of one comma five.
That's exactly what we're getting
this is a Q matrix with all the Q values,
and here we are getting the selected path.
So if your current state is one,
your best policy is to go from one to five.
Now, if you want to change your current state,
let's say we set the current state to two.
And before we run the code,
let's see which is the best possible way
to get to room number five from room number two.
From room number two, you can go to three,
then you can go to one, and then you can go to five.
This will give you a reward of hundred,
or you can go to room number three,
then go to four, and then go to five.
This will also give you a reward of hundred.
Our path should be something like that.
Let's save it and let's run the file.
So, basically, from stage two,
you're going to say three, then to four,
and then to five.
This is our best possible path
from two to room number five.
So, guys, this is exactly how
the Q learning algorithm works,
and this was a simple implementation
of the entire example that I just told you.
Now if any of you still have doubts
regarding Q learning or reinforcement learning,
make sure you comment them in the comment section,
and I'll try to answer all of your doubts.
No we're done with machine learning.
We've completed the whole machine learning model.
We've understood reinforcement learning,
supervised learning, unsupervised learning, and so on.
Before I'll get to deep learning,
I want to clear a very common misconception.
A lot of people get confused
between AI machine learning and deep learning,
because, you know, artificial intelligence,
machine learning and deep learning
are very common applications.
For example, Siri is an application
of artificial intelligence,
machine learning, and deep learning.
So how are these three connected?
Are they the same thing or how exactly
is the relationship between artificial intelligence,
machine learning, and deep learning?
This is what I'll be discussing.
now artificial intelligence is basically the science
of getting machines to mimic the behavior of human beings.
But when it comes to machine learning,
machine learning is a subset of artificial intelligence
that focuses on getting machines to make decisions
by feeding them data.
That's exactly what machine learning is.
It is a subset of artificial intelligence.
Deep learning, on the other hand,
is a subset of machine learning
that uses the concept of neural networks
to solve complex problems.
So, to sum it up, artificial intelligence,
machine learning, and deep learning,
are interconnected fields.
Machine learning and deep learning
aids artificial intelligence
by providing a set of algorithms and neural networks
to solve data-driven problems.
That's how AI, machine learning, and deep learning
are related.
I hope all of you have cleared your misconceptions
and doubts about AI, ML, and deep learning.
Now let's look at our next topic,
which is limitations of machine learning.
Now the first limitation is machine learning
is not capable enough to handle high dimensional data.
This is where the input and the output is very large.
So handling and processing such type of data
becomes very complex
and it takes up a lot of resources.
This is also sometimes known as the curse of dimensionality.
So, to understand this in simpler terms,
look at the image shown on this slide.
Consider a line of hundred yards
and let's say that you dropped a coin somewhere on the line.
Now it's quite convenient for you to find the coin
by simply walking along the line.
This is very simple because this line is considered
as single dimensional entity.
Now next, you consider that you have
a square of hundred yards,
and let's say you dropped a coin somewhere in between.
Now it's quite evident that you're going to take more time
to find the coin within that square
as compared to the previous scenario.
The square is, let's say, a two dimensional entity.
Let's take it a step ahead and let's consider a cube.
Okay, let's say there's a cube of 500 yards
and you have dropped a coin somewhere in between this cube.
Now it becomes even more difficult
for you to find the coin this time,
because this is a three dimensional entity.
So, as your dimension increases,
the problem becomes more complex.
So if you observe that the complexity
is increasing the increase in your dimensions,
and in real life, the high dimensional data
that we're talking about has thousands of dimensions
that makes it very complex to handle and process.
and a high dimensional data
can easily be found in used cases like image processing,
natural language processing, image translation, and so on.
Now in K-means itself,
we saw that we had 16 million possible colors.
That is a lot of data.
So this is why machine learning is restricted.
It cannot be used in the process of image recognition
because image recognition and images have a lot of pixels
and they have a lot of high dimensional data.
That's why machine learning becomes very restrictive
when it comes to such uses cases.
Now the second major challenge is to tell the computer
what are the features it should look for
that will play an important role
in predicted the outcome and in getting a good accuracy.
Now this process is something known as feature extraction.
Now feeding raw data to the algorithm rarely works,
and this is the reason why feature extraction
is a critical part of machine learning workflow.
Now the challenge for the programmer here increases
because the effectiveness of the algorithm
depends on how insightful the programmer is.
As a programmer,
you have to tell the machine that these are the features.
And depending on these features,
you have to predict the outcome.
That's how machine learning works.
So far, in all our demos,
we saw that we were providing predictor variables.
we were providing input variables
that will help us predict the outcome.
We were trying to find correlations between variables,
and we're trying to find out the variable
that is very important in predicting the output variable.
So this becomes a challenge for the programmer.
That's why it's very difficult to apply
machine learning model to complex problems
like object recognition, handwriting recognition,
natural language processing, and so on.
Now all these problems
and all these limitations in machine learning
led to the introduction of deep learning.
Now we're gonna discuss about deep learning.
Now deep learning is one of the only methods
by which we can overcome the challenges
of feature extraction.
This is because deep learning models
are capable of learning to focus
on the right features by themselves,
which requires very little guidance from the programmer.
Basically, deep learning mimics the way our brain functions.
That is it learns from experience.
So in deep learning, what happens is
feature extraction happens automatically.
You need very little guidance by the programmer.
So deep learning will learn the model,
and it will understand which feature or which variable
is important in predicting the outcome.
Let's say you have millions of predictor variables
for a particular problem statement.
How are you going to sit down and
understand the significance
of each of these predictor variables
it's going to be almost impossible
to sit down with so many features.
That's why we have deep learning.
Whenever there's high dimensionality data
or whenever the data is really large
and it has a lot of features
and a lot of predictor variables, we use deep learning.
Deep learning will extract features on its own
and understand which features are important
in predicting your output.
So that's the main idea behind deep learning.
Let me give you a small example also.
Suppose we want to make a system
that can recognize the face of different people
in an image.
Okay, so, basically, we're creating a system
that can identify the faces of different people in in image.
If we solve this by using
the typical machine learning algorithms,
we'll have to define facial features like eyes,
nose, ears, et cetera.
Okay, and then the system will identify
which features are more important for which person.
Now, if you consider deep learning for the same example,
deep learning will automatically find out the features
which are important for classification,
because it uses the concept of neural networks,
whereas in machine learning we have to
manually define these features on our own.
That's the main difference between deep learning
and machine learning.
Now the next question is how does deep learning work?
Now when people started coming up with deep learning,
their main aim was to re-engineer the human brain.
Okay, deep learning studies the basic unit of a brain
called the brain cell or a neuron.
All of you biology students
will know what I'm talking about.
So, basically, deep learning is inspired
from our brain structure.
Okay, in our brains, we have something known as neurons,
and these neurons are replicated in deep learning
as artificial neurons,
which are also called perceptrons.
Now, before we understand how artificial neural networks
or artificial neurons work,
let's understand how these biological neurons work,
because I'm not sure how many of you
are bio students over here.
So let's understand the functionality of biological neurons
and how we can mimic this functionality
in a perceptron or in an artificial neuron.
So, guys, if you loo at this image,
this is basically an image of a biological neuron.
If you focus on the structure of the biological neuron,
it has something known dendrites.
These dendrites are basically used to receive inputs.
Now the inputs are basically found in the cell body,
and it's passed on the next biological neuron.
So, through dendrites, you're going to receive signals
from other neurons, basically, input.
Then the cell body will sum up all these inputs,
and the axon will transmit this input to other neurons.
The axon will fire up through some threshold,
and it will get passed onto the next neuron.
So similar to this, a perceptron or an artificial neuron
receives multiple inputs,
and applies various transformations and functions
and provides us an output.
These multiple inputs are nothing but your input variables
or your predictor variables.
You're feeding input data to an artificial neuron
or to a perceptron,
and this perceptron will apply
various functions and transformations,
and it will give you an output.
Now just like our brain consists of
multiple connected neurons called neural networks,
we also build something known as
a network of artificial neurons
called artificial neural networks.
So that's the basic concept behind deep learning.
To sum it up, what exactly is deep learning?
Now deep learning is a collection of
statistical machine learning techniques
used to learn feature hierarchies based on the concept
of artificial neural networks.
So the main idea behind deep learning
is artificial neural networks
which work exactly like how our brain works.
Now in this diagram, you can see that
there are a couple of layers.
The first layer is known as the input layer.
This is where you'll receive all the inputs.
The last layer is known as the output layer
which provides your desired output.
Now, all the layers which are there between your input layer
and your output layer are known as the hidden layers.
Now, they can be any number of hidden layers,
thanks to all the resources that we have these days.
So you can have hundreds of hidden layers in between.
Now, the number of hidden layers
and the number of perceptrons in each of these layers
will entirely depend on the problem
or on the use case that you're trying to solve.
So this is basically how deep learning works.
So let's look at the example that we saw earlier.
Here what we want to do is we want to perform
image recognition using deep networks.
First, what we're gonna do is we are going to pass
this high dimensional data to the input layer.
To mach the dimensionality of the input data,
the input layer will contain
multiple sub layers of perceptrons
so that it consume the entire input.
Okay, so you'll have multiple sub layers of perceptrons.
Now, the output received from the input layer
will contain patterns and will only be able to identify
the edges of the images, based on the contrast levels.
This output will then be fed to hidden layer number one
where it'll be able to identify facial features
like your eyes, nose, ears, and all of that.
Now from here, the output will be fed
to hidden layer number two,
where it will be able to form entire faces
it'll go deeper into face recognition,
and this output of the hidden layer
will be sent to the output layer
or any other hidden layer that is there
before the output layer.
Now, finally, the output layer will perform classification,
based on the result that you'd get
from your previous layers.
So, this is exactly how deep learning works.
This is a small analogy that I use
to make you understand what deep learning is.
Now let's understand what a single layer perceptron is.
So like I said, perceptron is basically
an artificial neuron.
For something known as single layer
and multiple layer perceptron,
we'll first focus on single layer perceptron.
Now before I explain what a perceptron really is,
you should known that perceptrons are linear classifiers.
A single layer perceptron
is a linear or a binary classifier.
It is used mainly in supervised learning,
and it helps to classify the given input data
into separate classes.
So this diagram basically represents a perceptron.
A perceptron has multiple inputs.
It has a set of inputs labeled X one, X two,
until X n.
Now each of these input is given a specific weight.
Okay, so W one represents the weight of input X one.
W two represents the weight of input X two, and so on.
Now how you assign these weights
is a different thing altogether.
But for now, you need to know that each input
is assigned a particular weightage.
Now what a perceptron does is it computes some functions
on these weighted inputs, and it will give you the output.
So, basically, these weighted inputs
go through something known as summation.
Okay, summation is nothing but the product
of each of your input with its respective weight.
Now after the summation is done,
this passed onto transfer function.
A transfer function is nothing but an activation function.
I'll be discussing more about this in a minute.
The activation function.
And from the activation function,
you'll get the outputs Y one, Y two, and so on.
So guys, you need to understand four important parts
in a perceptron.
So, firstly, you have the input values.
You have X one, X two, X three.
You have something known as weights and bias,
and then you have something known as the net sum
and finally the activation function.
Now, all the inputs X
are multiplied with the respective weights.
So, X one will be multiplied with W one.
This is known as the summation.
After this, you'll add all the multiplied values,
and we'll call them as the weighted sum.
This is done using the summation function.
Now we'll apply the weighted sum
to a correct activation function.
Now, a lot of people have a confusion
about activation function.
Activation function is also known as the transfer function.
Now, in order to understand activation function,
this word stems from the way neurons
in a human brain work.
The neuron becomes activate
only after a certain potential is reached.
That threshold is known as the activation protection.
Therefore, mathematically,
it can be represented by a function
that reaches saturation after a threshold.
Okay, we have a lot of activation functions
like signum, sigmoid, tan, hedge, and so on.
You can think of activation function
as a function that maps the input
to the respective output.
And now I also spoke about weights and bias.
Now why do we assign weights to each of these inputs?
What weights do is they show a strength
of a particular input,
or how important a particular input
is for predicting the final output.
So, basically, the weightage of an input
denotes the importance of that input.
Now, our bias basically allows us
to shift the activation function
in order to get a precise output.
So that was all about perceptrons.
Now in order to make you understand perceptrons better,
let's look at a small analogy.
Suppose that you wanna go to a party
happening near your hose.
Now your decision will depend on a set of factors.
First is how is the weather.
Second probably is your wife, or your girlfriend,
or your boyfriend going with you.
And third, is there any public transport available?
Let's say these are the three factors
that you're going to consider before you go to a party.
So, depending on these predictor variables
or these features,
you're going to decide whether you're going to stay at home
or go and party.
Now, how is the weather is going to be your first input.
We'll represent this with a value X one.
Is your wife going with you is another input X two.
Any public transport is available
is your another input X three.
Now, X one will have two values, one and zero.
One represents that the weather is good.
Zero represents weather is bad.
Similarly, one represents that your wife is going,
and zero represents that your wife is not going.
And in X three, again, one represents that
there is public transport,
and zero represents that there is no public transport.
Now your output will either be one or zero.
One means you are going to the party,
and zero means you will be sitting at home.
Now in order to understand weightage,
let's say that the most important factor for you
is your weather.
If the weather is good,
it means that you will 100% go to the party.
Now if you weather is not good,
you've decided that you'll sit at home.
So the maximum weightage is for your weather variable.
So if your weather is really good,
you will go to the party.
It is a very important factor in order to understand
whether you're going to sit at home
or you're going to go to the party.
So, basically, if X one equal to one,
your output will be one.
Meaning that if your weather is good,
you'll go to the party.
Now let's randomly assign weights to each of our input.
W one is the weight associated with input X one.
W two is the weight with X two
and W three is the weight associated with X three.
Let's say that your W one is six,
your W two is two, and W three is two.
Now by using the activation function,
you're going to set a threshold of five.
Now this means that it will fire
when the weather is good
and won't fire if the weather is bad,
irrespective of the other inputs.
Now here, because your weightage is six,
so, basically, if you consider your first input
which has a weightage of six,
that means you're 100% going to go.
Let's say you're considering only the second input.
This means that you're not going to go,
because your weightage is two and your threshold is five.
So if your weightage is below your threshold,
it means that you're not going to go.
Now let's consider another scenario
where our threshold is three.
This means that it'll fire
when either X one is high
or the other two inputs are high.
Now W two is associated with your wife is going or not.
Let's say the weather is bad
and you have no public transportation,
meaning that your x one and x three is zero,
and only your x two is one.
Now if your x two is one,
your weightage is going to be two.
If your weightage is two,
you will not go because the threshold value is set to three.
The threshold value is set in such a way that
if X two and X three are combined together,
only then you'll go,
or only if x one is true, then you'll go.
So you're assigning threshold in such a way that
you will go for sure if the weather is good.
This is how you assign threshold.
This is nothing but your activation function.
So guys, I hope all of you understood,
the most amount of weightage
is associated with the input that is very important
in predicting your output.
This is exactly how a perceptron works.
Now let's look at the limitations of a perceptron.
Now in a perceptron, there are no hidden layers.
There's only an input layer,
and there is an output layer.
We have no hidden layers in between.
And because of this, you cannot classify
non-linearly separable data points.
Okay, if you have data, like in this figure,
how will you separate this.
You cannot use a perceptron to do this.
Alright, so complex problems that involve
a lot of parameters cannot be solved
by a single layer perceptron.
That's why we need something known as
multiple layer perceptron.
So now we'll discuss something known as
multilayer perceptron.
A multilayer perceptron has the same structure
of a single layer perceptron,
but with one or more hidden layer.
Okay, and that's why it's consider as a deep neural network.
So in a single layer perceptron,
we had only input layer, output layer.
We didn't have any hidden layer.
Now when it comes to multi-layer perceptron,
there are hidden layers in between,
and then there is the output layer.
It was in this similar manner, like I said,
first, you'll have the input X one, X two, X three,
and so on.
And each of these inputs will be assigned some weight.
W one, W two, W three, and so on.
Then you'll calculate the weighted summation
of each of these inputs and their weights.
After that, you'll send them to the transformation
or the activation function,
and you'll finally get the output.
Now, the only thing is that you'll have multiple
hidden layers in between,
one or more than one hidden layers.
So, guys, this is how a multilayer perceptron works.
It works on the concept of feed forward neural networks.
Feed forward means every node at each level
or each layer is connected to every other node.
So that's what feed forward networks are.
Now when it comes to assigning weights,
what we do is we randomly assign weights.
Initially we have input X one, X two, X three.
We randomly assign some weight W one, W two, W three,
and so on.
Now it's always necessary that whatever weights
we assign to our input,
those weights are actually correct,
meaning that those weights are company significant
in predicting your output.
So how a multilayer perceptron works is
a set of inputs are passed to the first hidden layer.
Now the activations from that layer are passed
through the next layer.
And from that layer, it's passed to the next hidden layer,
until you reach the output layer.
From the output layer, you'll form the two classes,
class one and class two.
Basically, you'll classify your input into
one of the two classes.
So that's how a multilayer perceptron works.
A very important concept the multiple layer perceptron
is back propagation.
Now what is back propagation.
Back propagation algorithm is
a supervised learning method for multilayer perceptrons.
Okay, now why do we need back propagation?
So guys, when we are designing a neural network
in the beginning, we initialize weights
with some random values, or any variable for that fact.
Now, obviously, we need to make sure that these weights
actually are correct,
meaning that these weights show the significance
of each predictor variable.
These weights have to fit our model
in such a way that our output is very precise.
So let's say that we randomly selected
some weights in the beginning,
but our model output is much more different
than our actual output,
meaning that our error value is very huge.
So how will you reduce this error.
Basically, what you need to do is
we need to somehow explain to the model
that we need to change the weight
in such a way that the error becomes minimum.
So the main thing is the weight and your error
is very highly related.
The weightage that you give to each input
will show how much error is there in your output,
because the most significant variables
will have the highest weightage.
And if the weightage is not correct,
then your output is also not correct.
Now, back propagation is a way to update your weights
in such a way that your outcome is precise
and your error is reduced.
So, in short back propagation is used to train
a multilayer perceptron.
It's basically use to update your weights
in such a way that your output is more precise,
and that your error is reduced.
So training a neural network is all about back propagation.
So the most common deep learning algorithm
for supervised training of the multilayer perceptron
is known as back propagation.
So, after calculating the weighted sum of inputs
and passing them through the activation function,
we propagate backwards and update the weights
to reduce the error.
It's as simple as that.
So in the beginning, you're going to assign some weights
to each of your input.
Now these inputs will go through the activation function
and it'll go through all the hidden layers
and give us an output.
Now when you get the output,
the output is not very precise,
or it is not the desired output.
So what you'll do is you'll propagate backwards,
and you start updating your weights
in such a way that your error
is as minimum as possible.
So, I'm going to repeat this once more.
So the idea behind back propagation
is to choose weights in such a way
that your error gets minimized.
To understand this, we'll look at a small example.
Let's say that we have a data set which has these labels.
Okay, your input is zero, one, two,
but your desired output is zero, one, and four
now the output of your model
when W equal to three is like this.
Notice the difference between your model output
and your desired output.
So, your model output is three,
but your desired output is two.
Similarly, when your model output is six,
your desired output is supposed to be four.
Now let's calculate the error when weight is equal to three.
The error is zero over here
because your desired output is zero,
and your model output is also zero.
Now the error in the second case is one.
Basically, your model output minus your desired output.
Three minus two, your error is one.
Similarly, your error for the third input is two,
which is six minus four.
When you take the square,
this is actually a very huge difference,
your error becomes larger.
Now what we need to do
is we need to update the weight value
in such a way that our error decreases.
Now here we've considered the weight as four.
So when you consider the weight as four,
your model output becomes zero, four, and eight.
Your desired output is zero, two, and four.
So your model output becomes zero, four, and eight,
which is a lot.
So guys, I hope you all know
how to calculate the output over here.
What I'm doing is I'm multiplying the input
with your weightage.
The weightage is four,
so zero into four will give me zero.
One into four will give me four,
and two into four will give me eight.
That's how I'm getting my model output over here.
For now, this is how I'm getting the output over here.
That's how you calculate your weightage.
Now, here, if you see that our desire output
is supposed to be zero, two, and four,
but we're getting an output of zero, four, and eight.
So our error is actually increasing
as we increase our weight.
Our error four W equal to four
have become zero, four, and 16,
whereas the error for W equal to three,
zero, one, and four.
I mean the square error.
So if you look at this, as we increase our weightage,
our error is increasing.
So, obviously, we know that
there is no point in increasing the value of W further.
But if we decrease the value of W,
our error actually decreases.
Alright, if we give a weightage of two,
our error decreases.
If we can find a relationship between our weight and error,
basically, if you increase the weight,
your error also increases.
If you decrease the weight, your error also decreases.
Now what we did here is we first initialize
some random value to W,
and then we propagated forward.
Then we notice that there is some error.
And to reduce that error, we propagated backwards
and increase the value of W.
After that, we notice that the error has increased,
and we came to know that we can't increase the w value.
Obviously, if your error is increasing
with increasing your weight,
you will not increase the weight.
So again, we propagated backwards,
and we decreased the W value.
So, after that, we noticed that the error has reduced.
So what we're trying is we're trying to get
the value of weight in such a way
that the error becomes as minimum as possible
so we need to figure out whether we need
to increase or decrease thew eight value.
Once we know that, we keep on updating the weight value
in that direction,
until the error becomes minimum.
Now you might reach a point where
if you further update the weight,
the error will again increase.
At that point, you need to stop.
Okay, at that point
is where your final weight value is there.
So, basically, this graph denotes that point.
Now this point is nothing but the global loss minimum.
If you update the weights further,
your error will also increase.
Now you need to find out where your global loss minimum is,
and that is where your optimum weight lies.
So let me summarize the steps for you.
First, you'll calculate the error.
This is how far your model output is
from your actual output.
Then you'll check whether the error
is minimized or not.
After that, if the error is very huge,
then you'll update the weight,
and you'll check the error again.
You'll repeat the process until the error becomes minimum
now once you reach the global loss minimum,
you'll stop updating the weights,
and we'll finalize your weight value.
This is exactly how back propagation works.
Now in order to tell you mathematically what we're doing
is we're using a method known as gradient descent.
Okay, this method is used
to adjust all the weights in the network
with an aim of reducing the error at the output layer.
So how gradient descent optimize our works is
the first step is you will calculate the error
by considering the below equation.
Here you're subtracting the summation of your actual output
from your network output.
Step two is based on the error you get,
you will calculate the rate of change of error
with respect to the change in the weight.
The learning rate is something that you set
in the beginning itself.
Step three is based on this change in weight,
you will calculate the new weight.
Alright, your updated weight will be your weight
plus the rate of change of weight.
So guys, that was all about
back propagation and weight update.
Now let's look at the limitations of feed forward network.
So far, we were discussing the multiple layer perceptron,
which uses the feed forward network.
Let's discuss the limitations of these
feed forward networks.
Now let's consider an example of image classification.
Okay, let's say you've trained the neural network
to classify images of various animals.
Now let's consider an example.
Here the first output is an elephant.
We have an elephant.
And this output will have nothing to do
with the previous output, which is a dog.
This means that the output at time T
is independent of the output at time T minus one.
Now consider this scenario
where you will require the use
of previously obtained output.
Okay, the concept is very similarly to reading a book.
As you turn every page, you need
an understanding of the previous pages
if you want to make sense of the information,
then you need to know what you learned before.
That's exactly what you're doing right now.
In order to understand deep learning,
you have to understand machine learning.
So, basically, with the feed forward network
the new output at time T plus one
has nothing to do with the output at time T,
or T minus one, or T minus two.
So feed forward networks cannot be used
while predicting a word in a sentence,
as it will have absolutely no relationship
with the previous set of words.
So, a feed forward network cannot be used in
use cases wherein you have to predict the outcome
based on your previous outcome.
So, in a lot of use cases,
your previous output will also determine your next output.
So, for such cases, you may not make use
of feed forward network.
Now, what modification can you make
so that your network can learn
from your previous mistakes.
For this, we have solution.
So, a solution to this is recurrent neural networks.
So, basically, let's say you have an input
at time T minus one,
and you'll get some output when you feed it to the network.
Now, some information from this input at T minus one
is fed to the next input,
which is input at time T.
Some information from this output
is fed into the next input,
which is input at T plus one.
So, basically, you keep feeding information
from the previous input to the next input.
That's how recurrent neural networks really work.
So recurrent networks
are a type of artificial neural networks
designed to recognize patterns in sequence of data,
such as text, genomes, handwriting, spoken words,
time series data, sensors, stock markets,
and government agencies.
So, guys, recurrent neural networks are actually
a very important part of deep learning,
because recurring neural networks have
applications in a lot of domains.
Okay, in time series and in stock markets,
the main network that I use
are recurrent neural networks,
because each of your inputs are correlated
now to better understand recurrent neural networks,
let's consider a small example
let's say that you go to the gym regularly,
and the trainer has given you
a schedule for your workout.
So basically, the exercises are repeated
after every third day.
Okay, this is what your schedule looks like.
So, make a note that all these exercises are repeated
in a proper order or in a sequence every week
first, let us use a feedforward network
to try and predict the type of exercises
that we're going to do.
The inputs here are Day of the week, the month,
and your health status.
Okay, so, neural network has to be trained
using these inputs to provide us with the prediction
of the exercise that we should do.
Now let's try and understand the same thing using
recurrent neural networks.
In recurrent neural networks,
what we'll do is we'll consider the inputs
of the previous day.
Okay, so if you did a shoulder workout yesterday,
then you can do a bicep exercise today,
and this goes on for the rest of the week.
However, if you happen to miss a day at the gym,
the data from the previously attended time stamps
can be considered.
It can be done like this.
So, if a model is trained based on the data
it can obtain from the previous exercise,
the output on the model will be extremely accurate.
In such cases, if you need to do know the output
at T minus one in order to predict the output at T.
In such cases, recurrent neural networks are very essential.
So, basically, I'm feeding some inputs
through the neural networks.
You'll go through a few functions,
and you'll get the output.
So, basically, you're predicting the output
based on past information or based on your past input.
So that's how recurrent neural networks work.
Now let's look at another type of neural network
known as convolutional neural network.
To understand why we need convolutional neural networks,
let's look at an analogy.
How do you think a computer reads an image?
Consider this image.
This is a New York skyline image.
On the first glance,
you'll see a lot of buildings and a lot of colors.
How does a computer process this image?
The image is actually broken down into three color channels,
which is the red, green, and blue.
It reads in the form of RGB values.
Now each of these color channels are mapped
with the image's pixel
then the computer will recognize the value
associated with each pixel,
and determine the size of the image.
Now for the black and white images,
there is only one channel,
but the concept is still the same.
The thing is we cannot make use of
fully connected networks when it comes to
convolutional neural networks.
I'll tell you why.
Now consider the first input image.
Okay, first image has size about
28 into 28 into three pixels.
And if we input this to a neural network,
we'll get about 2,352 weights
in the first hidden layer itself.
Now consider another example.
Okay, let's say we have an image
of 200 into 200 into three pixels.
So the size of your first hidden layer
becomes around 120,000.
Now if this is just the first hidden layer,
imagine the number of neurons that you need
to process an entire complex image set.
This leads to something known as overfitting,
because all of the hidden layers are connected.
They're massively connected.
There's connection between each and every node.
Because of this, we face overfitting.
We have way too much of data.
We have to use way too many neurons,
which is not practical.
So that's why we have something known as
convolutional neural networks.
Now convolutional neural networks,
like any other neural network
are made up of neurons with learnable weights and basis.
So each neuron receives several input.
It takes a weighted sum over them,
and it gets passed on through some activation function,
and finally responds with an output.
So, the concept in convolutional neural networks
is that the neuron in a particular layer
will only be connected to a small region
of the layer before it.
Not all the neurons will be connected
in a fully-connected manner,
which leads to overfitting
because we need way too many neurons
to solve this problem.
Only the regions, which are significant
are connected to each other.
There is no full connection
in convolutional neural networks.
So gus, what we did so far is we discussed
what a perceptron is.
We discussed the different types
of neural networks that are there.
We discussed a feedforward neural network.
We discuss multi layer perceptrons
we discussed recurrent neural networks,
and convolutional neural networks.
I'm not going to go too much in depth
with these concepts
now I'll be executing a demo.
If you you haven't understood any
theoretical concept of deep learning,
please let me know in the comment section.
Apart from this, I'll also leave
a couple of links in the description box,
so that you understand the whole download in a better way.
Okay, if you want a more in-depth explanation,
I'll leave a couple of links in the description box.
For now, what I'm gonna do is I'll be running
a practical demonstration to show you
what exactly download does
so, basically, what we're going to do in this demo
is we're going to predict stock prices.
Like I said, stock price prediction
is one of the very good applications
of deep neural networks.
You can easily predict the stock price
of a particular stock for the next minute
or the next day by using deep neural networks.
So that's exactly what we're gonna do in this demo
now, before I discuss the code,
let me tell you a few things about our data set.
The data set contains around 42,000 minutes
of data ranging from April to August 2017
on 500 stocks,
as well as the total S&P 500 Index price.
So the index and stocks are arranged
in a wide format.
So, this is my data set, data_stocks.
It's in the CSV format.
So what I'm gonna do is I'm going to use
the read CSV function in order to import this data set.
This is just the part of where my data set is stored.
This data set was actually cleaned and prepared,
meaning that we don't have any missing stock
and index prices.
So the file does not contain any missing values.
Now what we're gonna do first
is we'll drop the data valuable
we have a variable known as date,
which is not really necessary
in predicting our outcome over here.
So that's exactly what I'm doing here.
I'm just dropping the date variable.
So here, I'm checking the dimensions of the data set.
This is pretty understandable,
using the shape function to do that.
Now, always you make the data as a NymPy array.
This makes computation much easier.
The next process is the data splicing.
I've already discussed data the data splicing with you all.
Here we're just preparing the training
and the testing data.
So the training data will contain
80% of the total data set.
Okay, and also we are not shuffling the data set.
We're just slicing the data set sequentially.
That's why we have a test start start
and the test end variable.
In sequence, I'll be selecting the data.
There's no need of shuffling this data set.
These are stock prices
it does not make sense to shuffle this data.
Now in the next step, we're going to do is
we're going to scale the data
now, scaling data and data normalization
is one of the most important steps.
You cannot miss this step
I already mentioned earlier
what normalization and scaling is.
Now most neural networks
benefit from scaling inputs.
This is because most common activation function
of the networks neuron such as tan, hedge, and sigmoid.
Tan, hedge, and sigmoid are basically activation functions,
and these are defined in the range of minus one to one
or zero and one.
So that's why scaling is an important thing
in deep neural networks
for scaling, again, we'll use the MinMaxScaler.
So we're just importing that function over here.
And also one point to note is that
you have to be very cautious
about what part of data you're scaling
and when you're doing it.
A very common mistake is to scale the whole data set
before training and test splits are being applied.
So before data splicing itself,
you shouldn't be scaling your data.
Now this is a mistake because
scaling invokes the calculation of statistics.
For example, minimum or maximum range of the variable
gets affected.
So when performing time series forecasting in real life,
you do not have information from future observations
at the time of forecasting.
That's why calculation of scaling statistics
has to be conducted on training data,
and only then it has to be applied to the test data.
Otherwise, you're basically using the future information
at the time of forecasting,
which obviously going to lead to biasness
so that's why you need to make sure
you do scaling very accurately.
So, basically, what we're doing is the number of features
in the training data are stored
in a variable known as n stocks.
After this, we'll import the infamous TensorFlow.
So guys, TensorFlow is actually a very good
piece of software and it is currently the leading
deep learning and neural network computation framework.
It is based on a C++ low-level backend,
but it's usually controlled through Python.
So TensorFlow actually operates as
a graphical representation of your computations.
And this is important because neural networks
are actually graphs of data and mathematical operation.
So that's why TensorFlow is just perfect
for neural networks and deep learning.
So the next thing after importing the TensorFlow library
is something known as placeholders.
Placeholders are used to store, import, and target data.
We need two placeholders in order to fit our model.
So basically, X will contain the network's input,
which is the stock prices of all the stocks
at time T equal to T.
And y will contain the network's output,
which is the stock price at time T is equal to T plus one.
Now the shape of the X placeholder
means that the inputs are two-dimensional matrix.
And the outputs are a one-dimensional vector.
So guys, basically, the non-argument indicates
that at this point we do not yet know
the number of observations
that'll flow through the neural network.
We just keep it as a flexible array for now.
We'll later define the variable batch size
that controls the number of observations
in each training batch.
Now, apart form this, we also have
something know as initializers.
Now, before I tell you what these initializers are,
you need to understand that
there's something known as variables
that are used as flexible containers
that are allowed to change during the execution.
Weights and bias are represented as variables
in order to adapt during training.
I already discuss weights and bias with you earlier.
Now weights and bias is something
that you need to initialize before you train the model.
That's how we discussed it even while I was explaining
neural networks to you.
So here, basically, we make use of something known as
variant scaling initializer
and for bias initializer,
we make use of zeros initializers.
These are some predefined functions in our TensorFlow model.
We'll not get into the depth of those things.
Now let's look at our model architecture parameters.
So the next thing we have to discuss
is the model architecture parameters.
Now the model that we build,
it consists of four hidden layers.
For the first layer, we've assigned 1,024 neurons
which is likely more than double the size of the inputs.
The subsequent hidden layers are always
half the size of the previous layer,
which means that in the hidden layer number two,
we'll have 512 neurons.
Hidden layer three will have 256.
And similarly, hidden layer number four
will have 128 neurons.
Now why do we keep reducing the number of neurons
as we go through each hidden layer.
We do this because the number of neurons
for each subsequent layer compresses the information
that the network identifies in the previous layer.
Of course there are other possible network architectures
that you can apply for this problem statement,
but I'm trying to keep it as simple as possible,
because I'm introducing deep learning to you all.
So I can't build a model architecture
that's very complex and hard to explain.
And of course, we have output over here
which will be assigned a single neuron.
Now it is very important to understand
that variable dimensions between your input,
hidden, and output layers.
So, as a rule of thumb in multilayer perceptrons,
the second dimension of the previous layer
is the first dimension in the current layer.
So the second dimension in my first hidden layer
is going to be my first dimension in my second hidden layer.
Now the reason behind this is pretty logical.
It's because the output from the first hidden layer
is passed on as an input to the second hidden layer.
That's why the second dimension of the previous layer
is the same as the first dimension
of the next layer or the current layer.
I hope this is understandable.
Now coming to the bias dimension over here,
the bias dimension is always
equal to the second dimension of your current layer,
meaning that you're just going to pass
the number of neurons in that particular hidden layer
as your dimension in your bias.
So here, the number of neurons, 1,024,
you're passing the same number as a parameter to your bias.
Similarly, even for hidden layer number two,
if you see a second dimension here
is n_neurons_2.
I'm passing the same parameter over here as well.
Similarly, for hidden layer three
and hidden layer number four.
Alright, I hope this is understandable
now we come to the output layer.
The output layer will obviously have
the output from hidden layer number four.
This is our output from hidden layer four
that's passed as the first dimension in our output layer,
and it'll finally have your n target,
which is set to one over here.
This is our output.
Your bias will basically have the current layer's dimension,
which is n target.
You're passing that same parameter over here.
Now after you define the required weight
and the bias variables,
the architecture of the network has to be specified.
What you do is placeholders and variables
need to be combined into a system of
sequential matrix multiplication.
So that's exactly what's happening over here.
Apart from this, all the hidden layers
need to be transformed by using the activation function.
So, activation functions are important
components of the network
because they introduce non-linearity to the system.
This means that high dimensional data
can be dealt with with the help of the activation functions.
Obviously, we have very high dimensional data
when it comes to neural networks.
We don't have a single dimension
or we don't have two or three inputs.
We have thousands and thousands of inputs.
So, in order for a neural network to process
that much of high dimensional data,
we need something known as activation functions.
That's why we make use of activation functions.
Now, there are dozens of activation functions,
and one of the most common one
is the rectified linear unit,
rectified linear unit.
RELU is nothing but rectified linear unit,
which is what we're gonna be using in this model.
So, after, you applied the transformation function
to your hidden layer, you need to make sure that
your output is transposed.
This is followed by a very important function known as
cost function.
So the cost function of a network
is used to generate a measure of deviation
between the network's prediction
and the actual observed training targets.
So this is basically your actual output
minus your model output.
It basically calculates the error between your actual output
and your predicted output.
So, for regression problems, the mean squared error function
is commonly used.
I have discussed MSC, mean squared error, before.
So, basically, we are just measuring
the deviation over here.
MSC is nothing bot your deviation
from your actual output.
That's exactly what we're doing here.
So after you've computed your error,
the next step is obviously to update
your weight and your bias.
So, we have something known as the optimizers.
They basically take care of all the necessary computations
that are needed to adapt the network's weight
and bias variables during the training phase.
That's exactly what's happening over here.
Now the main function of this optimizer is that
it invoke something known as a gradient.
Now if you all remember, we discussed gradient before
it basically indicates the direction
in which the weights and the bias
has to be changed during the training
in order to minimize the network's cost function
or the network's error.
So you need to figure out whether you need to increase
the weight and the bias in order to decrease the error,
or is it the other way around?
You need to understand the relationship
between your error and your weight variable.
That's exactly what the optimizer does.
It invokes the gradient.
We will give you the direction in which the weights
and the bias have to be changed.
So now that you know what an optimizer does,
in our model, we'll be using
something known as the AdamOptimizer.
This is one of the current default optimizers
in deep learning.
Adam basically stands for adaptive moment estimation,
and it can be considered as a combination between
very two popular optimizers called Adagrad and RMSprop.
Now let's not get into the depth of the optimizers.
The main agenda here
is for you to understand the logic behind deep learning.
We don't have to go into the functions.
I know these are predefined functions
which TensorFlow takes care of.
Next we have something known as initializers.
Now, initializers are used to initialize
the network's variables before training.
We already discussed this before.
I'll define the initializer here again.
I've already done it earlier in this session.
Initializers are already defined.
So I just removed that line of code.
Next step would be fitting the neural network.
So after we've defined the place holders, the variables,
variables which are basically weights and bias,
the initializers, the cost functions,
and the optimizers of the network,
the model has to be trained.
Now, this is usually done by using
the mini batch training method,
because we have very huge data set.
So it's always best to use the mini batch training method.
Now what happens during mini batch training
is random data samples of any batch size
are drawn from the training data,
and they are fed into the network.
So the training data set gets divided into
N divided by your batch size batches
that are sequentially fed into the network.
So, one after the other,
each of these batches will be fed into the network.
At this point, the placeholder which are your X and Y,
they come into play.
They store the input and the target data
and present them to the network as inputs and targets.
That's the main functionality of placeholders.
What they do is they store the input and the target data,
and they provide this to the network
as inputs and targets.
That's exactly what your placeholders do.
So let's say that a sample data batch of X.
Now this data batch flows through the network
until it reaches the output layer.
There the TensorFlow compares the model's predictions
against the actual observed targets,
which is stored in Y.
If you all remember,
we stored our actual observed targets in Y.
After this, TensorFlow will conduct
something known as optimization step,
and it'll update the network's parameters
like the weight of the network and the bias.
So after having update your weight and the bias,
the next batch is sampled and the process gets repeated.
So this procedure will continue
until all the batches have presented to the network.
And one full sweep over all batches
is known as an epoch.
So I've defined this entire thing over here.
So we're gonna go through 10 epochs,
meaning that all the batches
are going to go through training,
meaning you're going to input each batch that is X,
and it'll flow through the network
until it reaches the output layer.
There what happens is TensorFlow
will compare your predictions.
That is basically what your model predicted
against the actual observed targets
which is stored in Y.
After this, TensorFlow will perform optimization
wherein it'll update the network paramters
like your weight and your bias.
After you update the weight and the bias,
the next batch will get sampled
and the process will keep repeating.
This happens until all the batches are
implemented in the network.
So what I just told you was one epoch.
We're going to repeat this 10 times.
So a batch size is 256,
meaning that we have 256 batches.
So here we're going to assign x and y,
what I just spoke to you about.
The mini batch training starts over here
so, basically, your first batch
will start flowing through the network
until it reaches the output layer.
After this, TensorFlow will compare your model's prediction.
This is where predictions happen.
It'll compare your model's prediction
to the actual observed targets
which is stored in y.
Then TensorFlow will start doing optimization,
and it'll update the network paramters
like your weight and your bias.
So after you update the weight and the biases,
the next batch will get input into the network,
and this process will keep repeating.
This process will repeat 10 times
because we've defined 10 epochs.
Now, also during the training,
we evaluate the network's prediction on the test set,
which is basically the data which we haven't learned,
but this data is set aside for every fifth batch,
and this is visualized.
So in our problem statement,
what a network is going to do
is it's going to predict the stock price
continuously over a time period of T plus one.
We're feeding it data about a stock price at time T.
It's going to give us an output of time T plus one.
Now let me run this code
and let's see how close our predicted values are
to the actual values.
We're going to visualize this entire thing,
and we've also exported this
in order to combine it into a video animation.
I'll show you what the video looks like.
So now let's look at our visualization.
We'll look at our output.
So the orange basically shows our model's prediction.
So the model quickly learns the shape
and the location of the time series in the test data
and showing us an accurate prediction.
It's pretty close to the actual prediction.
Now as I'm explaining this to you,
each batch is running here.
We are at epoch two.
We have 10 epochs to go over here.
So you can see that the network is actually adapting
to the basic shape of the time series,
and it's learning finer patterns in the data.
You see it keeps learning patterns
and the production is getting closer and closer
after every epoch.
So let just wait til we reach epoch 10
and we complete the entire process.
So guys, I think the predictions are pretty close,
like the pattern and the shape is learned very well
by our neural network.
It is actually mimicking this network.
The only deviation is in the values.
Apart from that, it's learning the shape
of the time series data in almost the same way.
The shape is exactly the same.
It looks very similar to me.
Now, also remember that there are a lot of ways
of improving your result.
You can change the design of your layers
or you can change the number of neurons.
You can choose different initialization functions
and activation functions.
You can introduce something known as dropout layers
which basically help you to get rid of overfitting,
and there's also something known as early stopping.
Early stopping helps you understand
where you must stop your batch training.
That's also another method that you can implement
for improving your model.
Now there are also different types of deep learning model
that you can use for this problem.
Here we use the feedforward network,
which basically means that the batches
will flow from left to right.
Okay, so our 10 epochs are over.
Now the final thing that's getting calculate is our error,
MSC or mean squared error.
So guys, don't worry about this warning.
It's just a warning.
So our mean square error comes down to 0.0029
which is pretty low because the target is scaled.
And this means that our accuracy is pretty good.
So guys, like I mentioned,
if you want to improve the accuracy of the model,
you can use different schemes,
you can use different initialization functions,
or you can try out different transformation functions.
You can use something known as dropout technique
and early stopping in order to make the training phase
even more better.
So guys, that was the end of our deep learning demo.
I hope all of you understood the deep learning demo.
For those of you who are just learning
deep learning for the first time,
it might be a little confusing.
So if you have any doubts regarding the demo,
let me know in the comment section.
I'll also leave a couple of links in the description box,
so that you can understand deep learning
in a little more depth.
Now let's look at our final topic for today,
which is natural language processing.
Now before we understand what text mining is
and what natural language processing is,
we have to understand the need for text mining
and natural language processing.
So guys, the number one reason why we need
text mining and natural language processing
is because of the amount of data
that we're generating during this time.
Like I mentioned earlier,
there are around 2.5 quintillion bytes of data
that is created every day,
and this number is only going to grow.
With the evolution of communication
through social media,
we generate tons and tons of data.
The numbers are on your screen.
These numbers are literally for every minute.
On Instagram, every minute, 1.7 million pictures are posted.
Okay, 1.7 or more than 1.7 million pictures are posted.
Similarly, we have tweets.
We have around 347,000 tweets every minute on Twitter.
This is actually a lot and lot of data.
So, every time we're using a phone,
we're generating way too much data.
Just watching a video on YouTube
is generating a lot of data.
When sending text messages from WhatsApp,
that is also generating tons and tons of data.
Now the only problem is not our data generation.
The problem is that out of all the data
that we're generating, only 21% of the data
is structured and well-formatted.
The remaining of the data is unstructured,
and the major source of unstructured data include
text messages from WhatsApp, Facebook likes,
comments on Instagram, bulk emails
that we send out ever single day.
All of this accounts for the unstructured data
that we have today.
Now the question here is what can be done
with so much data.
Now the data that we generate
can be used to grow businesses.
By analyzing and mining the data,
we can add more value to a business.
This exactly what text mining is all about.
So text mining or text analytics
is the analysis of data available to us
in a day-to-day spoken or written language.
It is amazing so much data that we generate
can actually be used in text mining.
We have data from word Word documents,
PowerPoints, chat messages, emails.
All of this is used to add value to a business
now the data that we get from sources
like social media, IoT,
they are mainly unstructured,
and unstructured data cannot be used
to draw useful insights to grow a business.
That's exactly why we need to text mining.
Text mining or text analytics
is the process of deriving meaningful information
from natural language text.
So, all the data that we generate through text messages,
emails, documents, files,
are written in natural language text.
And we are going to use text mining
and natural language processing
to draw useful insights or patterns from such data.
Now let's look at a few examples
to show you how natural language processing
and text mining is used.
So now before I move any further,
I want to compare text mining and NLP.
A lot of you might be confused
about what exactly text mining is
and how is it related to natural language processing.
A lot of people have also asked me
why is NLP and text mining
considered as one and the same
and are they the same thing.
So, basically, text mining is a vast field
that makes use of natural language processing
to derive high quality information from the text.
So, basically, text mining is a process,
and natural language processing is a method
used to carry out text mining.
So, in a way, you can say that text mining
is a vast field which uses and NLP
in order perform text analysis and text mining.
So, NLP is a part of text mining.
Now let's understand what exactly
natural language processing is.
Now, natural language processing
is a component of text mining
which basically helps a machine in reading the text.
Obviously, machines don't actually known English or French,
they interpret data in the form of zeroes and ones.
So this is where natural language processing comes in.
NLP is what computers and smart phones
use to understand our language,
both spoken and written language.
Now because use language to interact with our device,
NLP became an integral part of our life.
NLP uses concepts of computer science
and artificial intelligence
to study the data and derive useful information from it.
Now before we move any further,
let's look at a few applications of NLP and text mining.
Now we all spend a lot of time surfing the webs.
Have you ever notice that
if you start typing a word on Google,
you immediately get suggestions like these.
These feature is also known as auto complete.
It'll basically suggest the rest of the word for you.
And we also have something known as spam detection.
Here is an example of how Google recognizes
the misspelling Netflix
and shows results for keywords that match your misspelling.
So, the spam detection is also based
on the concepts of text mining
and natural language processing.
Next we have predictive typing and spell checkers.
Features like auto correct, email classification
are all applications of text mining and NLP.
Now we look at a couple of more applications
of natural language processing.
We have something known as sentimental analysis.
Sentimental analysis is extremely useful
in social media monitoring,
because it allows us to gain an overview
of the wider public opinion behind certain topics.
So, basically, sentimental analysis
is used to understand the public's opinion
or customer's opinion on a certain product
or on a certain topic.
Sentimental analysis is actually a very huge part
of a lot of social media platforms
like Twitter, Facebook.
They use sentimental analysis very frequently.
Then we have something known as chatbot.
Chatbots are basically the solutions
for all the consumer frustration,
regarding customer call assistance.
So we have companies like Pizza Hut, Uber
who have started using chatbots
to provide good customer service,
apart form that speech recognition.
NLP has widely been used in speech recognition.
We're all aware of Alexa, Siri, Google Assistant,
and Cortana.
These are all applications of natural language processing.
Machine translation is another important application of NLP.
An example of this is the Google Translator
that uses NLP to process and translate
one language to the other.
Other application include spell checkers,
keywords search, information extraction,
and NLP can be used to get useful information
from various website, from word documents,
from files, and et cetera.
It can also be used in advertisement matching.
This basically means a recommendation of ads
based on your history.
So now that you have a basic understanding of where
natural language processing is used
and what exactly it is,
let's take a look at some important concepts.
So, firstly, we're gonna discuss tokenization.
Now tokenization is the mos basic step in text mining.
Tokenization basically means breaking down data
into smaller chunks or tokens
so that they can be easily analyzed.
Now how tokenization works is
it works by breaking a complex sentence into words.
So you're breaking a huge sentence into words.
You'll understand the importance of each of the word
with respect to the whole sentence,
after which will produce a description
on an input sentence.
So, for example, let's say we have this sentence,
tokens are simple.
If we apply tokenization on this sentence,
what we get is this.
We're just breaking a sentence into words.
Then we're understanding the importance
of each of these words.
We'll perform NLP process on each of these words
to understand how important each word
is in this entire sentence.
For me, I think tokens and simple are important words,
are is basically another stop word.
We'll be discussing about stop words in our further slides.
But for now, you eed to understand that tokenization
is a very simple process that involves
breaking sentences into words.
Next, we have something known as stemming.
Stemming is basically normalizing words
into its base form or into its root form.
Take a look at this example.
We have words like detection,
detecting, detected, and detections.
Now we all know that the root word
for all these words is detect.
Basically, all these words mean detect.
So the stemming algorithm works by cutting off the end
or the beginning of the word
and taking into account a list of common prefixes
and suffixes that can be found on any word.
So guys, stemming can be successful in some cases,
but not always.
That is why a lot of people affirm that
stemming has a lot of limitations.
So, in order to overcome the limitations of stemming,
we have something known as lemmatization.
Now what lemmatization does is
it takes into consideration the morphological analysis
of the words.
To do so, it is necessary to have a detailed dictionary
which the algorithm can look through to link the form
back to its lemma.
So, basically lemmatization
is also quite similar to stemming.
It maps different words into one common root.
Sometimes what happens in stemming is that
most of the words gets cut off.
Let's say we wanted to cut detection into detect.
Sometimes it becomes det or it becomes tect,
or something like that.
So because of this, the grammar
or the importance of the word goes away.
You don't know what the words mean anymore.
Due to the indiscriminate cutting of the word,
sometimes the grammar the understanding of the word
is not there anymore.
So that's why lemmatization was introduced.
The output of lemmatization is always going to be
a proper word.
Okay, it's not going to be something that is half cut
or anything like that.
You're going to understand the morphological analysis
and then only you're going to perform lemmatization.
An example of a lemmatizer
is you're going to convert gone, going, and went into go.
All the three words anyway mean the same thing.
So you're going to convert it into go.
We are not removing the first and the last part of the word.
What we're doing is we're understanding
the grammar behind the word.
We're understanding the English
or the morphological analysis of the word,
and only then we're going to perform lemmatization.
That's what lemmatization is all about.
Now stop words are basically a set of
commonly used words in any language, not just English.
Now the reason why stop words
are critical to many applications is that
if we remove the words that are very commonly used
in a given language,
we can finally focus on the important words.
For example, in the context of a search engine,
let's say you open up Google
and you try how to make strawberry milkshake.
What the search engine is going to do is
it's going to find a lot more pages
that contain the terms how to make,
rather than pages which contain the recipe
for your strawberry milkshake.
That's why you have to disregard these terms.
The search engine can actually focus
on the strawberry milkshake recipe,
instead of looking for pages that have how to and so on.
So that's why you need to remove these stop words.
Stop words are how to, begin, gone, various, and, the,
all of these are stop words.
They are not necessarily important
to understand the importance of the sentence.
So you get rid of these commonly used words,
so that you can focus on the actual keywords.
Another term you need to understand
is document term matrix.
A document term matrix is basically a matrix
with documents designated by roles and words by columns.
So if your document one has this sentence, this is fun,
or has these word, this is fun,
then you're going to get one, one, one over here.
In document two, if you see we have this and we have is,
but we do not have fun.
So that's what a document term matrix is.
It is basically to understand whether your document
contains each of these words.
It is a frequency matrix.
That is what a document term matrix is.
Now let's move on and look at
a natural language processing demo.
So what we're gonna do is we're gonna perform
sentimental analysis.
Now like I said, sentimental analysis
is one of the most popular applications
of natural language processing.
It refers to the processing of determining
whether a given piece of text or a given sentence of text
is positive or negative.
So, in some variations, we consider
a sentence to also be neutral.
That's a third option.
And this technique is commonly used to discover
how people feel about a particular topic
or what are people's opinion about a particular topic.
So this is mainly used to analyze the sentiments of users
in various forms,
such as in marketing campaigns, in social media,
in e-commerce websites, and so on.
So now we'll be performing sentimental analysis
using Python.
So we are going to perform natural language processing
by using the NaiveBayesClassifier.
That's why we are importing the NaiveBayesClassifier.
So guys, Python provides a library known
as natural language toolkit.
This library contains all the functions that are needed
to perform natural language processing.
Also in this library,
we have a predefined data set called movie reviews.
What we're gonna do is we're going to download that
from our NLTK, which is natural language toolkit.
We're basically going to run our analysis
on this movie review data set.
And that's exactly what we're doing over here.
Now what we're doing is we're defining a function
in order to extract features.
So this is our function.
It's just going to extract all our words.
Now that we've extracted the data,
we need to train it,
so we'll do that by using our movie reviews data set
that we just downloaded.
We're going to understand
the positive words and the negative words.
So what we're doing here is we're just loading our positive
and our negative reviews.
We're loading both of them.
After that, we'll separate each of these
into positive features and negative features.
This is pretty understandable.
Next, we'll split the data
into our training and testing set.
Now this is something that we've been doing
for all our demos.
This is also known as data splicing.
We've also set a threshold factor of 0.8
which basically means that 80% of your data set
will belong to your training,
and 20% will be for your testing.
You're going to do this even for your positive
and your negative words.
After that, you're just extracting the features again,
and you're just printing
the number of training data points that you have.
You're just printing the length of your training features
and you're printing the length
of your testing features.
We can see the output, let's run this program.
So if you see that we're getting
the number of training data points as 1,600
and your number of testing data points are 400,
there's an 80 to 20% ration over here.
After this, we'll be using the NaiveBayesClassifier
and we'll define the object
for the NaiveBayesClassifier with basically classifier,
and we'll train this using our training data set.
We'll also look at the accuracy of our model.
The accuracy of our classifier is around 73%,
which is a really good number.
Now this classifier object will actually contain
the most informative words
that are obtained during analysis.
These words are basically essential in understanding
which word is classified as positive
and which is classified as negative.
What we're doing here is we're going to review movies.
We're going to see which movie review is positive
or which movie review is negative.
Now this classifier will basically have
all the informative words that will help us decide
which is a positive review or a negative review.
Then we're just printing these 10 most informative words,
and we have outstanding, insulting,
vulnerable, ludicrous, uninvolving,
avoids, fascination, and so on.
These are the most important words in our text.
Now what we're gonna do is we're gonna test our model.
I've randomly given some reviews.
If you want, let's add another review.
We'll say
I loved the
movie.
So I've added another review over here.
Here we're just printing the review,
and we're checking if this is a positive review
or a negative review.
Now let's look at our predictions.
We'll save this and...
I forgot to put a comma over here.
Save it and let's run the file again.
So these were our randomly written movie reviews.
The predicted sentiment is positive.
Our probability score was 0.61.
It's pretty accurate here.
This is a dull movie and I would never recommend it,
is a negative sentiment.
The cinematography is pretty great,
that's a positive review.
The movie is pathetic is obviously a negative review.
The direction was terrible,
and the story was all over the place.
This is also considered as a negative review.
Similarly, I love the movie is what I just inputted,
and I've got a positive review on that.
So our classifier actually works really well.
It's giving us good accuracy
and it's classifying the sentiments very accurately.
So, guys, this was all about sentimental analysis.
Here we basically saw if a movie review
was positive or negative.
So guys, that was all for our NLP demo.
I hope all of you understood this.
It was a simple sentimental analysis
that we saw through Python.
So again, if you have doubts,
please leave them in the comment section,
and I'll help you with all of the queries.
So guys, that was our last module,
which was on natural language processing.
Now before I end today's session,
I would like to discuss with you
the machine learning engineers program
that we have Edureka.
So we all are aware of
the demand of the machine learning engineer.
So, at Edureka, we have a master's program
that involves 200-plus hours of interactive training.
So the machine learning master's program at Edureka
has around nine modules and 200-plus hours
of interactive learning.
So let me tell you the curriculum
that this course provides.
So your first module will basically cover
Python programming.
It'll have all the basics and all your data visualization,
your GUI programming, your functions,
and your object-oriented concepts.
The second module will cover machine learning with Python.
So you'll supervise algorithms
and unsupervised algorithms
along with statistics and time series
in Python will be covered in your second module.
Your third module will have graphical modeling.
This is quite important when ti comes to machine learning.
Here you'll be taught about decision making,
graph theory, inference, and Bayesian and Markov's network,
and module number four will cover
reinforcement learning in depth.
Here you'll understanding dynamic programming,
temporal difference, Bellman equations,
all the concepts of reinforcement learning in depth.
All the detail in advance concepts
of reinforcement learning.
So, module number five will cover NLP with Python.
You'll understand tokenization, stemming lemmatization,
syntax, tree parsing, and so on.
And module number six will have module six will have
artificial intelligence and deep learning with TensorFlow.
This module is a very advanced version
of all your machine learning
and reinforcement learning that you'll learn.
Deep learning will be in depth over here.
You'll be using TensorFlow throughout.
They'll cover all the concepts that we saw, CNN, RNN.
it'll cover the various type of neural networks,
like convolutional neural networks,
recurrent neural networks,
long, short-term memory, neural networks,
and auto encoders and so on.
The seventh module is all about PySpark.
It'll show you how Spark SQL works
and all the features and functions of Spark ML library.
And the last module will finally cover
about Python Spark using PySpark.
Appropriate from this seven modules,
you'll also get two free self-paced courses.
Let's actually take a look at the course.
So this is your machine learning
engineer master's program.
You'll have nine courses, 200-plus hours
of interactive learning.
This is the whole course curriculum,
which we just discussed.
Here there are seven modules.
Apart from these seven modules,
you'll be given two free self-paced courses,
which I'll discuss shortly.
You can also get to know the average annual salary
for a machine learning engineer,
which is over $134,000.
And there are also a lot of job openings
in the field of machine learning AI and data science.
So the job titles that you might get
are machine learning engineer, AI engineer,
data scientist, data and analytics manger,
NLP engineer, and data engineer.
So this is basically the curriculum.
Your first will by Python programming certification,
machine learning certification using Python,
graphical modeling, reinforcement learning,
natural language processing,
AI and deep learning with TensorFlow.
Python Spark certification training using PySpark.
If you want to learn more about each of these modules,
you can just go and view the curriculum.
They'll explain each and every concept
that they'll be showing in this module.
All of this is going to be covered here.
This is just the first module.
Now at the end of this project,
you will be given a verified certificate of completion
with your name on it,
and these are the free elective courses
that you're going to get.
One is your Python scripting certification training.
And the other is your Python Statistics
for Data Science Course.
Both of these courses explain Python in depth.
The second course on statistics
will explain all the concepts
of statistics probability, descriptive statistics,
inferential statistics,
time series, testing data,
data clustering, regression modeling, and so on.
So each of the module is designed in such a way that
you'll have a practical demo
or a practical implementation
after each and every model.
So all the concept that I theoretically taught to you
will be explained through practical demos.
This way you'll get a good understanding of
the entire machine learning and AI concepts.
So, if any of you are interested
in enrolling for this program
or if you want to learn more about
the machine learning course offered by Edureka,
please leave your email IDs in the comment section,
and we'll get back to you
with all the details of the course.
So guys, with this, we come to the end
of this AI full course session.
I hope all of you have understood the basic concepts
and the idea behind AI machine learning, deep learning,
and natural language processing.
So if you still have doubts
regarding any of these topics,
mention them in the comment section,
and I'll try to answer all your queries.
So guys, thank you so much for joining me in this session.
Have a great day.
I hope you have enjoyed listening to this video.
Please be kind enough to like it,
and you can comment any of your doubts and queries,
and we will reply them at the earliest.
Do look out for more videos in our playlist
and subscribe to Edureka channel to learn more.
Happy learning.