Another little step towards the machine learning: A first lesson about R language

Hi Guys,
Welcome Back!

Today another little step towards the machine learning with a first lesseon about the R language.              

Introduction

Yes, you remember very well!
We already talked about SQL Server and the R language some posts ago.

In a first post we talked about how to install the machine learning services in SQL Server
While in a second post we talked briefly about using R language to read data from SQL Server

Now if you want to do another step towards the machine learning you really need to learn a bit of R language.

So today I will show some very basic concepts about this really powerful and widely used in data science, the R language.

We will se how to do and assignment, how to use array, vector and matrix.

Are you Ready?

Let's go!

A Basic lesson about R!

R is a very powerful language and it is also free and expandible through varius library.

I suppose you have already installed R and so you a ready to execute the R Console.

You can start typing some after the ">" prompt

You can, for example, type the text below and then press enter:


> 8+2

You will obtain:

[1] 4


Type now:

> log(2)

and you will receive:

[1] 0.6931472


Ok R is a fantastic calculator!!! But let’s continue...

Variables

Some note:

• R declare automatically variables
• The assignment is done with the <- command
• R is case sensitive
  

You can declare a variable a and assign the value 4 typing:

> a <- 4

Now if you type:

> a

You will obtain the result of the variable "a"

[1] 4 

Vectors (Arrays)

R can manage vectors (array) in an easy way

Type for example the command below:

List <- c(1, 2, 2.5, 9, 9, 9, 5, 2)

Through the “c” concatenate command you declare a Vector

In order to show the content og the vector just type:

> List

[1] 1.0 2.0 2.5 9.0 9.0 9.0 5.0 2.0


Nice!

You can also get a subset of your vector with this syntax:

> List [1:3]

[1] 1.0 2.0 2.5


Or you can easily sum the values of all the elements of your vector:

sum(List) [1] 440.5

Another way to declare a vector is this:

> W <- vector(length = 2)

> W[1] <- 10

> W[2] <- 12

And now i will show you how to manage Matrix!


Matrix

You can declare a matrix through this Syntax:

> Mat <- matrix(nrow = 8, ncol = 4)

To display the Matrix content:

> Mat

[,1][ ,2][ ,3][ ,4]

[1,] NA NA NA NA

[2,] NA NA NA NA

[3,] NA NA NA NA

[4,] NA NA NA NA

[5,] NA NA NA NA

[6,] NA NA NA NA

[7,] NA NA NA NA

[8,] NA NA NA NA

And set a value with:

Mat [1, 1] <- 2.0

That’s all for today!

I hope you liked this post and found it useful.

Luca

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