View source for R/C2/Creating-Matrices-using-Data-Frames/English

'''Title of script''': Creating Matrices using Data Frames 

'''Author''': Shaik Sameer (IIIT Vadodara) and Sudhakar Kumar (IIT Bombay)

'''Keywords''': R, RStudio, matrices, data frames, transpose, determinant, video tutorial.

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|'''Visual Cue'''
|'''Narration'''
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|| Show slide 

Opening slide
|| Welcome to the spoken tutorial on '''Creating Matrices using Data Frames.'''
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Learning Objectives
|| In this tutorial, we will learn how to: 
* Convert a '''data frame''' into a '''matrix'''
* Create a '''matrix''' in '''R'''
* Perform basic operations on '''matrices''' 

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Pre-requisites

spoken-tutorial.org
|| To understand this tutorial, you should know,
* '''Data frames''' and '''Vectors''' in '''R'''
* '''Basics''' of '''Matrices'''
* '''R script''' in '''RStudio'''
* How to set '''working directory''' in '''RStudio'''

If not, please locate the relevant tutorials on '''R''' on this website.
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System Specifications

|| This tutorial is recorded on
* '''Ubuntu Linux '''OS version''' 16.04'''
* '''R '''version''' 3.4.4'''
* '''RStudio''' version''' 1.1.456'''

Install '''R''' version '''3.2.0''' or higher. 
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Download Files 
||For this tutorial, we will use the '''data frame CaptaincyData.csv''' and a '''script '''file '''myMatrix.R'''.

Please download these files from the '''Code files''' link of this tutorial.
|- 
|| [Computer screen]

Highlight '''CaptaincyData.csv '''and '''myMatrix.R''' in the folder '''Matrices '''
|| I have downloaded and moved these files to '''Matrices''' folder in '''myProject''' folder on the '''Desktop'''. 

I have also set '''Matrices''' folder as my '''Working Directory.''' 
|- 
|| 
|| Let us switch to '''RStudio'''.
|- 
|| Click '''myMatrix.R''' in '''RStudio'''

Point to''' myMatrix.R''' in '''Rstudio.'''
|| Open the '''script myMatrix.R''' in '''RStudio'''.

For this, click on the '''script myMatrix.R''' 

'''Script myMatrix.R''' opens in '''RStudio'''.
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|| Highlight '''rm''' in '''Source '''window
|| Here, I have used '''rm function''' to remove all existing variables from memory. 

This prevents errors such as use of older data. 
|- 
|| Highlight '''Source''' button

Highlight '''captaincy''' in the '''Source''' window 
|| Run this '''script''' by clicking on the '''Source '''button. 

The captaincy '''data frame''' is displayed in the '''Source''' window. 
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|| Show slide 

Data in Matrix Format
|| We need our data in a '''matrix''' form to:
* Calculate the inverse of a '''matrix'''
* Perform '''matrix''' operations like addition, subtraction, multiplication, etc.

Hence, we need to learn how to convert a '''data frame''' into a '''matrix'''.
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|| 
|| Let us get back to '''RStudio'''. 
|- 
|| [RStudio]

Highlight the three rows of '''captaincy'''

|| We will convert the values in first three rows of '''played''', '''won''' and '''lost''' columns into a '''matrix'''. 

We will create a '''subset''' for extracting these values.
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|| Highlight '''myMatrix.R '''in the '''Source''' window 
|| Click on the '''script myMatrix.R'''
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|| [RStudio]
'''subdata <- captaincy[1:3, c("played", "won", "lost")]'''

|| In the '''Source '''window, type the following command Press '''Enter'''.

I am resizing the '''Source''' window.

Press '''Enter''' to go to the next line. 

Press '''Enter''' at the end of every command. 
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|| [RStudio]

Highlight '''1:3''' in the '''Source '''window 

Highlight '''c''' in the '''Source '''window 
|| '''1 colon 3''' indicates that the first three rows are to be extracted. 

'''c''' is the '''concatenate vector command''' with names of each column within double quotes. 
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|| Press '''Ctrl + S''' >> Press '''Ctrl+Enter''' keys.
|| Save the '''script''' and execute the current line. 
|- 
|| [RStudio]

Highlight '''subData '''in the '''Environment''' window.

Click on the arrow before '''subData'''.
|| The variable '''subData''' appears in the '''Environment''' window. 

Click on the arrow before '''subData''' to expand its contents. 
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|| 
|| Now, we will convert this '''subset''' into a '''matrix'''.
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|| [RStudio]

'''matrixA <- as.matrix(subdata)'''
|| In the '''Source''' window, type '''matrixA''' then press '''Alt''' and '''hyphen'''(-)keys simultaneously.

Now type '''as'''dot '''matrix''', within parentheses type '''subdata''' and press '''Enter'''. 
|- 
|| Highlight '''as.matrix''' in the '''Source''' window
|| '''as.matrix function''' is used to convert the '''subdata '''into a '''matrix'''. 
|- 
|| [RStudio]

'''print(matrixA) '''
|| In '''Source''' window, type '''print''', within '''parentheses''' '''matrixA'''. 
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|| Press '''Ctrl + S''' >> Highlight two lines >> Press '''Ctrl+Enter''' keys.
|| Save the '''script''' and run these two lines. 
|- 
|| Highlight the output in the '''Console''' window
|| The content of '''matrixA''' is shown on the '''Console''' window.
|- 
|| cursor on the interface.
|| Now let us create a 3 by 3 '''identity matrix'''.

Create a '''vector''' named '''values''' containing the row-wise values of a 3 by 3 identity matrix.
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|| [RStudio]

'''values <- c(1,0,0,0,1,0,0,0,1)'''
|| In the '''Source''' window, type the following command and press '''Enter'''. 
|- 
|| [RStudio]

'''matrixB <- matrix(values, nrow = 3, ncol = 3, byrow = TRUE)'''
|| Now we will create a variable '''matrixB''' to store the '''matrix''' created using vector values.

In the '''Source''' window, type the following command. Press '''Enter'''.

Press '''Enter''' to go to the next line. 
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|| [RStudio]

Highlight '''values''' in the '''Source''' window

Highlight '''nrow''' and '''ncol''' in the '''Source''' window

Highlight '''byrow''' in the '''Source''' window 
|| Here, I have used '''matrix function''' with following '''arguments''':
* data of '''values''' vector
* number of rows as '''nrow''' equal to '''3'''
* number of columns as '''ncol''' equal to ''' 3''' 
* '''byrow '''equal to''' TRUE''' indicates that, data provided has to be arranged row-wise in the '''matrix'''. 

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|| [RStudio]

'''print(matrixB)'''
|| Now, type '''print''' within parentheses type '''matrixB''' to show the contents of the '''matrix'''. 
|- 
|| Press''' Ctrl + S''' keys >> Highlight three lines >> Press '''Ctrl + Enter''' keys 
|| Save the '''script''' and run the last three lines of code.
|- 
|| Highlight the output in the '''Console''' window
|| The '''identity matrix''' is shown on the '''Console''' window. 
|- 
|| Cursor on the interface.
|| Now let us perform some arithmetic operations on '''matrices'''.
|- 
|| Highlight the boundary of '''Source''' window 
|| I will resize the '''Source''' window. 
|- 
|| [RStudio]

'''matrixA + matrixB'''

'''matrixA - matrixB '''
|| We will add and subtract '''matrices A''' and '''B'''.

In the '''Source''' window, type '''matrixA''' space '''plus''' sign space '''matrixB'''.

Next, type '''matrixA''' space '''minus''' sign space ''' ''matrixB'''
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|| Press '''Ctrl + S''' >> Press '''Ctrl+Enter''' keys.

Highlight the output on the '''Console''' window
|| Save the '''script''' and run these two lines. 

I will resize the '''Console''' window to see the output properly. 

The resulting '''matrices''' are shown on the '''Console''' window. 
|- 
|| [RStudio]

'''matrixA * matrixB '''
|| Let us perform multiplication of individual '''elements''' of two '''matrices'''.

In the '''Source''' window, type '''matrixA''' space '''asterisk''' sign space '''matrixB'''
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|| Press '''Ctrl + S''' >> Press '''Ctrl + Enter''' keys.

Highlight the output on the '''Console''' window.
|| Save the '''script''' and run the current lines. 

The resulting '''matrix''' is shown on the '''Console''' window. 
|- 
|| Highlight '''matrixA''' and '''matrixB''' in '''Environment''' window
|| Now, we will perform a true '''matrix''' multiplication with these '''matrices'''. 

1st row of '''matrixA''' is multiplied by 1st column of '''matrixB'''. 

Hence number of columns of '''matrixA''' should be equal to the number of rows of '''matrixB'''. 
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|| '''matrixA %*% matrixB '''
|| In the '''Source''' window, type '''matrixA''' space '''percentage''' sign '''asterisk percentage''' sign  space '''matrixB'''. 
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|| Press '''Ctrl + S''' >> Press '''Ctrl+Enter''' keys.

Highlight the output on the '''Console''' window.
|| Save the '''script''' and run the current line. 

The resulting '''matrix''' is shown on the '''Console''' window. 
|- 
|| Cursor on the interface.
|| Now let us calculate the '''transpose''' and '''determinant''' of '''matrixA'''.
|- 
|| [RStudio]'''t(matrixA)'''

'''det(matrixA)'''
|| In the '''Source''' window, type '''t''' and '''matrixA''' in parentheses. 

Now, type '''det''' and '''matrixA''' in parentheses. 
|- 
|| Press '''Ctrl + S''' >> Press '''Ctrl+Enter''' keys.

Highlight the output on the '''Console''' window.
|| Save the '''script''' and run these two lines. 

The corresponding output is shown on the '''Console''' window. 
|- 
|| 
|| Let us summarize what we have learnt.
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Summary
|| In this tutorial, we have learnt how to: 
* Convert a '''data frame''' into a '''matrix'''
* Create a '''matrix''' in '''R'''
* Perform basic operations on '''matrices'''

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Assignment

|| We now suggest an assignment.
* Consider 2 '''vectors''' c(9,10,11,12) and c(13,14,15,16). 
* Create a 4 by 2 '''matrix''' from these two '''vectors'''. 

For solution, please refer to the '''Additional materials''' section on this website. 
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About the Spoken Tutorial Project
|| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.
|- 
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Spoken Tutorial Workshops
|| We conduct workshops using Spoken Tutorials and give certificates.

Please contact us.
|- 
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Forum to answer questions
|| Please post your timed queries in this forum.
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Forum to answer questions
|| Please post your general queries in this forum.
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Textbook Companion
|| The '''FOSSEE ''' team coordinates the '''TBC '''project.

For more details, please visit these sites.
|- 
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Acknowledgement
|| The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India
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Thank You
|| The script for this tutorial was contributed by Shaik Sameer (FOSSEE Fellow 2018).

This is Sudhakar Kumar from IIT Bombay signing off. Thanks for watching.
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