Sudhakarst at 10:54, 24 April 2019

2019-04-24T10:54:53Z

Nancyvarkey: Created page with ''''FOSS:''' R through RStudio R version 3.0.0 (2013-04-03) and RStudio version 0.97.336 '''Tutorial Title:''' Introduction to data frames in …'

2013-10-10T07:51:25Z

Created page with ''''FOSS:''' R through RStudio R version 3.0.0 (2013-04-03) and RStudio version 0.97.336 '''Tutorial Title:''' Introduction to data frames in …'

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'''FOSS:''' R through RStudio

          R version 3.0.0 (2013-04-03) and RStudio version 0.97.336

'''Tutorial Title:''' Introduction to data frames in R

'''Author:''' Kannan Moudgalya

'''Reviewer: ''' Jayendran Venkateswaran, Neeraj Hatekar, S. Subramanian, T. Santhanam, Sanjeev Bakshi, Revathi Kasturi and others

'''Date:''' 14 September 2013

'''Keywords: ''' Video tutorial, spoken tutorial, data frames, csv file, data display, importing csv files

'''Files required:''' None

'''Immediate prerequisite in the same family: '''
Introduction to basics of R

'''Prerequisite from any other family of ST: '''
None

{|Border=1
!Visual Cue
!Narration
|-
|Slide 1

Opening slide
|Welcome to the spoken tutorial on introduction to '''data frames''' in '''R'''.

I am Kannan Moudgalya.

|-
|Slide 2

Learning Objectives

|In this tutorial, we will explain

* how to create a '''data frame''' in '''R'''
* how to work with it
* how to save it into a file and
* how to read data from a file into a '''data frame'''

We will also learn about the '''data sets''' that come with the '''R''' software

|-
|Slide 3

Prerequisites

|To understand this tutorial,
* One needs to know elementary maths
* ''for example, the meaning of mean, row and column''
* One needs to know how to edit a text file and plotting
* No programming background is required, however
* Anyone with a simple exposure to '''statistics''' can understand this tutorial

|-
|Prerequisites (Ctd)

|
* Please locate this tutorial on our web page, '''spoken hyphen tutorial dot org'''
* Prerequisite spoken tutorials, if any, will be mentioned in this page

|-
|Slide 4

Systems Requirements

|
* I am using version '''3''' of '''R'''
* '''RStudio 0.97'''
* and '''Mac OS X 10.7'''

But it should work in other versions and also other operating systems.

|-
|RStudio, Slide 6
|Let us switch to '''RStudio'''.

|-
|<nowiki>sample <- c(-2,1,5.8)</nowiki>

|Let us begin with the '''“c” command''' to create a '''vector'''

Notice that I am using the '''assignment operator''', that is, '''less than''' followed by '''hyphen'''.

I will use the word '''get''' to denote this '''assignment'''.

This is the way to create a '''vector''' of three '''elements'''.

'''c''' stands for '''create''' or '''concatenate'''.

Although the '''equal to''' sign works most of the time, one usually uses this '''operator''' in '''R'''.

|-
|sample
|Let us view what the '''vector sample '''contains.

|-
|
|Let us now build a '''data set'''.

We will also call it as a '''data frame''' in this tutorial.

|-
|<nowiki>names <- c(“Mahi”,”Sourav”,”Azhar”,</nowiki>

“Sunny”,”Pataudi”,”Dravid”)

|Let me create a '''vector''' of Indian Cricket Captains, old and new.

'''names gets c of Mahi, Sourav, Azhar, Sunny, Pataudi, Dravid'''

Each name has to be entered in between '''double quotes'''.

|-
|names
|Let us view what the variable '''names '''contains.

|-
|
|I will create a '''vector''' to store the number of matches they captained.

One can see that all the '''variables''' got entered in the '''workspace.'''

|-
|<nowiki>captaincy <- dataframe(names,Y, played,won,lost)</nowiki>

|Now, let us put these together and create a '''data frame''' as I do now.

It is '''data dot frame'''.

|-
|View(captaincy)

|Let us understand what the command '''data frame '''does.

To do this, let us '''View brackets captaincy'''.

|-
|
|The contents of the '''data frame''' appear nicely in the window above.

|-
|
|What will happen if you just type '''captaincy''', without the '''View command'''?

Would you want to try it now?

|-
|
|In '''statistics''', one works with such '''data sets'''.

Remember, the '''commands''' and '''variables''' in '''R''' are case sensitive.

The '''View command''' begins with a '''capital V'''.

|-
|captaincy$names

|It is easy to access the parts of a '''data frame'''.

For example, this is how I will get the names in the '''captaincy data frame'''.

|-
|captaincy$won

captaincy$played

<nowiki>ratio <- captaincy$won / captaincy$played</nowiki>

|Let us similarly get the number of matches won.

Let us find the ratio of matches won.

When we divide a '''vector''' by another, '''R''' carries out component-wise division.

|-
|<nowiki>captaincy$victory <- ratio</nowiki>

|Let us include this ratio also in the '''captaincy data frame'''.

'''captaincy dollar victory''' gets '''ratio'''.

What is in '''ratio''' gets transferred to '''victory''', a variable in the '''data frame captaincy'''.

|-
|View(captaincy)

|We can check that ratio is included in captaincy by the '''View command'''.

We can see that the '''ratio''' is included in victory.

|-
|options(digits=2)

|Let us reduce the number of digits displayed in the ratio to 2.

We do this with the '''command options within brackets digits=2'''.

|-
|View(captaincy)
|Let us view '''captaincy.'''

We can see that it has been reduced to two digits.

|-
|captaincy$played
|Let us see the number of matches played by all the captains.

|-
|mean(captaincy$played)
|Let us find the '''mean''' of these matches.

|-
|(45+49+47+47+40+25) / 6

|By direct calculation, we find that '''mean''' does exactly what it should.

These two are equal.

|-
|

plot(captaincy$Y,ratio)

|Let us now get some plots with this '''data frame'''.

Let us plot the ratio of victories vs. the year of captaincy.

Remember that the '''x''' axis variable has to be listed first in the '''plot''' command.

|-
|plot(captaincy$names,captaincy$played)
|Let us plot the number of matches captained versus the names of the captains.

|-
|
|Drag this a little bit. The graph expands. Put it back.

|-
|
|We will now explain how to write this '''data fram'''e to a '''comma separated variable''' file or '''C S V'''.

|-
|write.csv(captaincy,”NewCaptaincy.csv”)

|We will use the command '''write.csv''', as we do now.

Let me move this to the right.

This writes the '''captaincy data frame''' into the file '''NewCaptaincy.csv'''

|-
|emacs NewCaptaincy.csv

|Let me open this file using my favourite text editor, '''emacs'''.

|-
|
|You may use any other text editor, such as '''notepad''' or '''vi''' or '''gedit'''.

Please do not, however, use '''Microsoft office''' or '''LibreOffice Writer''' for this purpose.

Because, you may not be able to load these files into '''R'''.

|-
|On the emacs editor...

|Let us now see what the file '''NewCaptaincy.csv''' contains.

This '''csv''' file contains everything that we created.

It also contains row numbers in every row, at the beginning.

|-
|write.csv(captaincy,

”NewCaptaincy.csv”,row.names=FALSE)
|How will you get rid of these row numbers?

Add an additional flag called '''row dot names equals FALSE'''.

|-
|
|Let us read the new version of this file.

In '''emacs''', I just have to refresh it.

In other editors, you may have to re-open the file.

We see that the row numbers no longer appear.
|-
|Change '''Mahi''' to '''Dhoni''' and save.

|Let us make a small change in this '''csv''' file and read it.

Let us change '''Mahi''' to '''Dhoni''' and save the file.

|-
|Workspace -> Import Dataset

|Let us click '''Import Dataset'''.

There are two options:
*from the text file and
*from the web.

Reading from a local file is a fool-proof method.

It works even if '''Internet''' is not available.

All one has to do is to download the required files ahead of time.

|-
|read a text file

View(NewCaptaincy)

|Let us click the '''File''' option.

Let us select '''NewCaptaincy.'''

In order to see this, let us maximise this, let us press '''Import''', let us press unmaximise.

You will not have this problem, of course, because, you will be using the whole screen.

For this tutorial, I am using only a small portion of the screen.

And that’s why we have had this problem.

The appearance of a data frame called '''NewCaptaincy''' here, and also here, shows that it has been read.

It also has '''Dhoni''' as the name.

The row numbers have also disappeared.

|-
|
|It is also possible to read '''excel '''and '''ods''' files into '''R'''.

This involves a little more work and hence not covered in this tutorial.

It is easy to export '''excel''' and '''ods''' files into '''csv''' format.

So, for now, please use the '''csv''' route to import '''excel''' or '''ods''' files.

|-
|

data()

|Let us take up the final topic for this tutorial.

'''R''' comes with several '''data frames'''.

To access them, issue the command '''data brackets'''.

'''R''' shows a list of available '''data frames'''.

We can carry out all sorts of calculations on these '''data sets'''.

|-
|View(CO2)
|We will just view one '''data set''', called '''C O 2'''.

|-
|
|We will conclude this tutorial here.

|-
|Slide 14

Summary

|In this tutorial, we learnt the following:
* We created '''vectors'''
* We put the '''vectors''' into a '''data frame'''
* We operated on the '''data frame'''
* We saved the '''data frame''' into a file
* Imported the file into '''R'''
* Examined the '''data frames''' that came with '''R'''

|-
|Slide 15

Assignment

|We now suggest an assignment.

* Find out how to calculate '''median''' using the '''help''' button.
* Repeat the above using web search.
* Calculate the '''mean''' and '''median''' of the '''data frame C O 2'''.
* Take '''R'''’s help for all the commands shown in this tutorial.
* Import a '''data set''' from the Internet directly or through a file.

|-
|Slide 16

About the Spoken Tutorial Project
|This video summarises the Spoken Tutorial project.

If you do not have good bandwidth, you may download and watch it.

|-
|Slide 17

Spoken Tutorial Workshops

|We conduct workshops using Spoken Tutorials; give Certificates.

Please contact us.

|-
|Slide 18

Acknowledgements
|The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India

|-
|Slide 19 Thanks
|Thanks for joining, goodbye.

|}

R/C2/Introduction-to-Data-Frames-in-R/English - Revision history

Sudhakarst at 10:54, 24 April 2019

Nancyvarkey: Created page with ''''FOSS:''' R through RStudio R version 3.0.0 (2013-04-03) and RStudio version 0.97.336 '''Tutorial Title:''' Introduction to data frames in …'