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.
| Visual Cue | Narration |
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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:
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Pre-requisites spoken-tutorial.org |
To understand this tutorial, you should know,
If not, please locate the relevant tutorials on R on this website. |
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System Specifications |
This tutorial is recorded on
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. |
| 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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Data in Matrix Format |
We need our data in a matrix form to:
Hence, we need to learn how to convert a data frame into a matrix. |
| 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. |
| Highlight myMatrix.R in the Source window | Click on the script myMatrix.R |
| [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. |
| [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. |
| 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. |
| Now, we will convert this subset into a matrix. | |
| [RStudio]
matrixA <- as.matrix(subdata) |
In the Source window, type matrixA then press Alt and hyphen(-)keys simultaneously.
Now type asdot 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. |
| 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. |
| [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. |
| [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:
|
| [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 |
| 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 |
| 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. |
| matrixA %*% matrixB | In the Source window, type matrixA space percentage sign asterisk percentage sign space matrixB. |
| 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:
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Assignment |
We now suggest an assignment.
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. |
