View source for R/C2/Operations-on-Matrices-and-Data-Frames/English-timed



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|'''Time'''
|'''Narration'''

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|| 00:01
|| Welcome to the spoken tutorial on '''Operations on Matrices and Data Frames'''.

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|| 00:08
|| In this tutorial, we will learn how to: 

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|| 00:13
|| Perform operations on '''matrices''' 

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|| 00:16
|| Add rows or columns to a '''data frame'''

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|| 00:20
|| To understand this tutorial, you should know

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|| 00:24
|| '''Data frames''' and '''Matrices''' in '''R''' 

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|| 00:27
|| '''R script '''in''' RStudio'''

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|| 00:32
||How to set working directory in '''RStudio''' 

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|| 00:37
|| If not, please locate the relevant tutorials on '''R''' on this website.

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|| 00:44
|| This tutorial is recorded on

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|| 00:47
|| '''Ubuntu Linux''' OS version 16.04

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|| 00:53
|| '''R''' version 3.4.4

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|| 00:58
|| '''RStudio''' version 1.1.456

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|| 01:05
|| Install''' R''' version 3.2.0 or higher. 

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|| 01:10
|| For this tutorial, we will use the '''data frame CaptaincyData.csv '''and the '''script '''file '''myMatrix.R'''.

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|| 01:21
|| Please download these files from the '''Code files''' link of this tutorial.

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|| 01:28
|| I have downloaded and moved these files to '''MatrixOps '''folder' in '''myProject''' folder on the '''Desktop'''. 

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|| 01:39
|| I have also set '''MatrixOps''' folder as my '''Working directory'''. 

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|| 01:46
|| Let us switch to '''Rstudio'''.

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|| 01:51
|| Open the '''script myMatrix.R''' in '''RStudio.'''

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|| 01:56
|| For this, click on the '''script myMatrix.R''' 

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|| 02:02
|| '''Script myMatrix.R '''opens in''' Rstudio.'''

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|| 02:08
|| Recall that, we had created a matrix named '''matrixA.'''

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|| 02:14
|| This '''matrix''' was extracted as a subset from the '''captaincy data frame'''. 

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|| 02:21
|| We will use '''matrixA''' here also. 

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|| 02:25
|| Run this '''script myMatrix.R''' to load the values in the '''Workspace'''. 

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|| 02:32
|| '''captaincy data frame''' opens in the '''Source''' window. 

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|| 02:37
|| I will resize the '''Source''' window. 

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|| 02:41
|| Now let us learn how to find the inverse of '''matrixA'''. 

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|| 02:48
|| Click on the''' script myMatrix.R'''

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|| 02:53
|| In the '''Source''' window, type '''solve, '''within parentheses''' matrixA'''. 

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|| 03:00
|| Press '''Enter'''. Press '''Enter''' at the end of every command. 

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|| 03:07
|| Save the '''script''' and run this line.

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|| 03:12
|| The inverse of '''matrixA''' in shown in the '''Console '''window. 

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|| 03:18
|| For more information on calculating inverse of a '''matrix''' in '''R''', please refer to the '''Additional materials''' section on this website.
|- 
|| 03:29
|| Now let us calculate the sum of all the '''elements''' in '''matrixA'''.

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|| 03:36
|| First, we shall use '''nested for loops''' for calculating this sum. 

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|| 03:43
|| Also, we shall estimate the time taken to calculate the sum in this way.

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|| 03:50
|| Let us add a '''comment - Calculating sum using for loop '''in the '''script'''. 

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|| 03:57
|| In the '''Source''' window, type '''# hash''' space '''Calculating sum using for loop'''. 
 
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|| 04:05
|| Press '''Enter'''. To calculate the time taken, we record the present time. 

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|| 04:12
|| In the '''Source''' window, type '''start Time''' with capital T.

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|| 04:18
|| Then press '''Alt '''and '''-'''('''hyphen''') keys simultaneously. 

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|| 04:23
|| Next, type''' Sys''' dot '''time''' followed by '''parentheses'''. 

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|| 04:30
|| '''Sys.time()''' is used to find the absolute date-time value in the current time. 

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|| 04:38
|| Let us initialise a '''variable totalSum'''. 

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|| 04:43
|| In the '''Source''' window, type '''totalSum''' 

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|| 04:47
|| then press '''Alt '''and''' -'''('''hyphen''') keys simultaneously. Then type zero. 

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|| 04:55
|| This '''variable''' will store the sum of '''elements''' in '''matrixA'''. 

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|| 05:01
|| Now, we will create two '''for loops''' to iterate through the rows and columns of the '''matrixA'''.

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|| 05:10
|| In the '''Source''' window, type '''for '''in parentheses''' i''' space '''in''' space 1 '''colon '''3 space

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|| 05:21
|| Now type opening curly bracket. '''RStudio''' automatically adds a closing curly bracket.

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|| 05:30
|| Press '''Enter''' just after the opening curly bracket and type the following '''command'''. 

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|| 05:39
|| Press '''Enter''' after the closing curly bracket of outer '''loop for(i in 1:3)'''. 

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|| 05:48
|| In the '''Source''' window, type '''print totalSum''' in''' parentheses'''. 

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|| 05:54
|| Now, we record the current time again. 

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|| 05:59
|| Type '''endTime '''then press '''Alt '''and '''-'''('''hyphen''') keys simultaneously. Type '''Sys''' dot '''time''' parentheses. 

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|| 06:10
|| Press '''Enter'''. Type '''endTime '''space minus sign space''' startTime''' to know the total time taken.
And save the '''script'''.

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|| 06:23
|| I am resizing the '''Source '''window.

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|| 06:27
|| Run the block of code from the '''comment line Calculating sum using for loop '''to the end. 

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|| 06:35
|| The '''totalSum''' is evaluated to be 237.

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|| 06:41
|| The time taken to calculate the sum of '''elements''' in '''matrixA''' using '''for loop''' is approximately 8 milliseconds. 

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|| 06:51
|| However, it may vary from system to system. 

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|| 06:56
|| Now, let us calculate the sum of all '''elements''' in '''matrixA''' using the '''sum function'''. 

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|| 07:05
|| We shall estimate the time taken to calculate the sum in this way also. 

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|| 07:12
|| In the script '''myMatrix.R''', add a '''comment Calculating sum using inbuilt function'''. 

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|| 07:21
|| In the '''Source''' window, type '''# hash''' space '''Calculating sum using inbuilt function'''.

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|| 07:30
|| Now, type the following '''commands'''. 

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|| 07:35
|| Save the '''script''' and run the block of code from the '''comment line Calculating sum using inbuilt function '''to the end. 

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|| 07:46
|| The time taken to calculate the sum of '''elements''' using '''sum function''' is 1.6 milliseconds. 

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|| 07:56
|| Whereas, it took 8 milliseconds to calculate the same sum using '''for loop'''. 

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|| 08:04
|| So, it is advisable to use '''inbuilt functions''' of '''R'''. 

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|| 08:10
|| Let us learn how to calculate sum of each '''row''' and sum of each '''column'''. 

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|| 08:18
|| In the '''Source''' window, type '''rowSums matrixA '''in parentheses.

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|| 08:26
|| Next, type''' colSums matrixA '''in parentheses.

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|| 08:32
|| Save the '''script''' and run these two lines to see the corresponding sums on the '''Console'''.

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|| 08:40
|| I am resizing the '''Console '''window to see the output properly. 

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|| 08:47
|| Now let us learn how to add rows and columns to an existing '''data frame'''.

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|| 08:55
|| Click on the '''captaincy data frame'''. 

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|| 08:59
|| Let us add a new row to the '''captaincy data frame.''' 

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|| 09:04
|| Click on the''' script myMatrix.R'''

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|| 09:09
|| In the '''Source''' window, type the following '''command'''. Press '''Enter '''.

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|| 09:24
|| Press '''Enter '''after the comma for better visibility. 

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|| 09:30
|| I am resizing the '''Source '''window

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|| 09:34
|| We have used '''rbind() function''' with the following '''arguments'''

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|| 09:40
|| name of the '''data frame''' to which we want to add the new row. Here, it is '''captaincy'''. 

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|| 09:48
|| the row to be added as an '''argument''' to '''data.frame()'''.

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|| 09:54
|| To '''data.frame() function''', we provide the values according to the columns of the actual '''data frame'''.

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|| 10:03
|| '''names''' = “Kohli”

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|| 10:06
|| '''Y''' = 2016

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|| 10:10
|| '''played''' = 30 

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|| 10:13
|| '''won''' = 20

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|| 10:17
|| '''lost''' = 9

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|| 10:20
|| '''victory''' = 20/30

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|| 10:24
|| In the '''Source''' window, type '''View '''within''' parentheses captaincy''' 

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|| 10:30
|| Save the '''script''' and run the last two lines of code. 

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|| 10:37
|| One new row with the details of '''Kohli''' is added in the '''captaincy data frame'''. 

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|| 10:44
|| Now let us create a new column named '''defeat''' in the '''captaincy data frame'''. 

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|| 10:52
|| Click on the '''script myMatrix.R'''. 

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|| 10:57
|| In the '''Source''' window, type the following '''command'''. 

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|| 11:03
|| Press '''Enter'''. Now we add '''defeat''' as a new column in '''captaincy data frame'''. 

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|| 11:11
|| In the '''Source''' window, type the following '''command''' Press '''Enter'''. 

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|| 11:17
|| We have used '''cbind() function''' with following two '''arguments''':

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|| 11:23
|| name of the '''data frame''' to which we want to add the new column. 

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|| 11:28
|| Here, it is '''captaincy'''.  name of the column to be added. Here, it is '''defeat'''. 

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|| 11:37
|| Now type '''View, captaincy '''in''' parentheses '''

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|| 11:42
|| Save the '''script''' and run the block of code starting from the declaration of '''defeat '''to the end.

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|| 11:52
|| '''defeat''' column is added in the '''captaincy data frame'''. 

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|| 11:58
|| Let us summarize what we have learnt.

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|| 12:04
|| In this tutorial, we have learned how to:

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|| 12:07
||  Perform operation on '''matrices''' 

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|| 12:11
|| Add rows or columns to a '''data frame'''

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|| 12:16
|| We now suggest an assignment.

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|| 12:20
|| Consider 2 '''vectors''' (9,10,11,12) and (13,14,15,16). 
 
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|| 12:30
|| Create a 4 by 2 '''matrix''' from these two '''vectors'''. 

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|| 12:35
|| Add another '''vector''' (17,18,19,20) as a column to the previous '''matrix'''.

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|| 12:45
|| For solutions, please refer to the '''Additional materials''' section on this website.

|- 
|| 12:52
|| The video at the following link summarises the Spoken Tutorial project.

|-
|| 12:58
|| Please download and watch it.

|- 
|| 13:01
|| We conduct workshops using Spoken Tutorials and give certificates. Please contact us.

|- 
|| 13:11
|| Please post your timed queries in this forum.

|- 
|| 13:16
|| Please post your general queries in this forum.

|- 
|| 13:21
|| The '''FOSSEE '''team coordinates the '''TBC '''project. For more details, please visit these sites.

|- 
|| 13:30
|| The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India

|- 
|| 13:37
|| The script for this tutorial was contributed by Shaik Sameer (FOSSEE Fellow 2018).

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|| 13:46
|| This is Sudhakar Kumar from IIT Bombay signing off. 

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|| 13:51
|| Thanks for watching.

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|}