View source for R/C2/Indexing-and-Slicing-Data-Frames/English-timed



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||'''Time'''
||'''Narration'''
 
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|| 00:01
|| Welcome to the spoken tutorial on '''Indexing and Slicing Data Frames'''. 

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

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|| 00:12
|| Extract '''rows''' or '''columns''' from a '''data '''frame

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|| Create a '''subset''' from a''' data frame'''

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|| Retrieve '''data '''using double square brackets

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|| 00:25 
|| To understand this tutorial, you should have knowledge about 

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|| '''Data frames''' in''' R''' 

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|| '''R''' '''script '''in '''RStudio '''and

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|| How to set '''Working directory''' in''' RStudio'''

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

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|| This tutorial is recorded on

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|| '''Ubuntu Linux '''OS version''' 16.04'''

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|| '''R '''version''' 3.2.3'''

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|| '''RStudio''' version''' 1.1.456'''

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|| Install '''R''' version '''3.2.0''' or higher.

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|| 01:14
|| For this tutorial, we will use the '''data frame CaptaincyData.csv''' and a '''script '''file '''mydataframe.R'''. 

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|| 01:25
|| Download these files from the '''Code files''' link of this tutorial.

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|| 01:31
|| I have downloaded and moved these files to the folder '''myProject''' on my '''Desktop'''. 

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|| 01:39
|| I have also set this folder as my '''Working Directory.''' 

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|| 01:45
||Let us switch to '''Rstudio'''.

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|| Let us open the '''script mydataframe.R''' in '''RStudio.'''

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|| For this, click on the '''script mydataframe.R'''. 

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|| 02:01
|| '''Script mydataframe.R '''opens in '''Rstudio.'''
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|| 02:07
|| Here, we have declared a''' variable captaincy''' to store and read '''CaptaincyData.csv'''.

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|| Also, '''View function''' is being used to see the contents of the file.

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|| 02:23
|| Remember, you may also use '''equal''' to sign in place of '''less than''' symbol followed by '''hyphen'''. 

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|| 02:32
|| However, we recommend '''less than''' symbol followed by '''hyphen'''.

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|| 02:38
|| For this, there is a shortcut in '''RStudio'''. 

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|| 02:42
|| Suppose we want to assign a value of 2 to a variable named '''testvar'''. 

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|| In the '''Console''' window, type '''testvar''' and then press 

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|| ''Alt '''and '''-'''('''hyphen''')''' '''keys simultaneously.

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|| Then type 2 and press '''Enter'''. 

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|| Let us get back to the '''Source''' window. 

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|| Run the '''script''' '''mydataframe.R''' by clicking on the '''Source''' button. 

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|| Now let us extract the contents of the third row of the '''captaincy data frame'''. 

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|| Click on '''script''' '''mydataframe.R'''
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|| In the '''Source '''window, type '''captaincy '''

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|| Type '''capt''' and press '''Enter '''to make the variable '''captaincy '''autocomplete. Now''' '''within square brackets 3 followed by '''comma. '''And press '''Enter'''. 

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|| Press '''Enter '''key''' '''at the end of every command. 

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|| Remember one of the most important features of '''RStudio''' include intelligent auto-completion of function names, packages, and R objects. 

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|| We use a '''comma''' within square brackets when we wish to extract a '''row'''.

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|| Save the '''script '''and execute the current line by pressing '''Ctrl+Enter''' keys.

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|| The third row of the '''captaincy data frame''' is seen in the '''Console''' window. 

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|| Now, let us run the same '''command''' without a '''comma'''. 

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|| In the '''Source '''window, type '''captaincy '''then''' '''within square brackets 3'''. '''

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|| Save the '''script '''and run this line only, as shown earlier.

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|| The contents of the third '''column''' of the '''data frame, '''are displayed on the '''Console '''window.

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|| So, to extract a '''column''', we shouldn’t use a '''comma''' within the square brackets.



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|| When we extract '''data''' using row number or column number, it is known as numeric indexing. 

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|| In the '''Source '''window, click on the '''captaincy data frame'''. 

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|| Let us now extract the contents of second and third '''rows''' of the '''captaincy''' '''data frame'''.

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|| To retrieve more than one '''row''', we use a numeric '''index vector'''. Click on the '''script mydataframe.R'''

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

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|| '''c''' '''function '''is being used to concatenate the second and third '''rows'''.

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|| Save the''' script''' and execute the current line. 

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|| The second and third '''rows''' of '''captaincy data frame''' are seen in the '''Console''' window. 

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|| In the '''Source '''window, click on the '''captaincy data frame'''. 

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|| Now, we’ll find who has played 25 matches from the '''played''' column of '''captaincy data frame'''. 

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|| Extracting this type of information is known as logical indexing. 

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|| Click on the '''script mydataframe.R'''

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|| In the '''Source '''window, type '''captaincy'''
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|| Within square brackets '''captaincy '''dollar sign '''played '''equal to equal to 25 '''comma. '''Press '''Enter'''.

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|| Remember, '''dollar''' sign allows you to extract '''elements''' by name. 

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|| Please note that there is no space between the two equal to signs. 

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|| Save the '''script''' and execute the current line. 

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|| The details of '''captain Dravid '''are shown in the '''Console''' window.

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|| In the '''Source '''window, click on the '''captaincy data frame'''. 

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|| Now let us learn how to get the values of any particular '''attribute''' for all the players.

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|| We will fetch the '''names '''of all the captains.

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|| For this, we need to know the values in the first '''column'''. 

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|| Click on the '''script mydataframe.R'''

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|| In the '''Source '''window, type '''captaincy '''and''' '''within square brackets '''1'''.

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|| Please note that I have not used a '''comma''' inside the square brackets. 

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|| Save the '''script''' and execute the current line. 
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|| The '''names''' of the captains are seen in the '''Console''' window. 

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|| Usually we use column '''names''' instead of column numbers.

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|| To know the names of the captains, type '''captaincy. '''

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|| Within square brackets inside double quotes '''names'''

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|| Save the '''script''' and execute the current line. 

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|| Names of the captains are shown in the '''Console''' window. 

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|| Extracting '''data''' by column names is known as name indexing. 

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|| 08:23
|| Clear the '''Console''' window by clicking on the broom icon. 

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|| In the '''Source '''window, click on the '''captaincy data frame'''

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|| Now let us view the names of the captains along with the number of matches they have won.

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|| Click on the '''script mydataframe.R'''

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

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|| Here''' c''' '''function '''is used''' '''to concatenate '''names '''and '''won'''. 

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|| Observe that''' names''' and '''won''' have been written within double quotes. 

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|| Save the '''script''' and execute this line. 

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|| The '''names''' of captains and the number of matches '''won '''are seen in the '''Console''' window.

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|| 09:18
|| Now let us extract a '''subset '''from '''captaincy data frame'''.

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|| We will create a '''subset''' of captains,''' '''who have won more than 30% of their matches. 

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|| This is called slicing a '''data frame'''. 

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|| In the '''Source '''window, click on the '''captaincy data frame'''. 

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|| Please note that there is a '''column''' named '''victory''' in the '''captaincy''' '''data frame.'''

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|| For required '''subset '''of captains, their victory should be greater than 0.3. 

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|| For this '''subset''', we shall only show the 

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|| names

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|| number of matches '''played'''

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|| number of matches '''won'''

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|| Click on the '''script mydataframe.R'''

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|| I will resize the '''Source''' window. 

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|| In the '''Source '''window, type '''the following command'''

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|| Now, press '''Enter '''after the comma followed by 0 point 3. 

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|| You can press '''Enter''' after a''' comma''' for better visibility. 

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|| The''' select parameter''' is used to select the required columns, '''names''', '''played''', and '''won'''. 

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|| In the '''Source '''window, type '''print''' within '''parentheses subData '''.

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|| Save the '''script''' and run these two lines. 

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

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|| The '''subData '''is shown in the '''Console''' window.

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|| In the '''Source '''window, click on the '''captaincy data frame'''. 

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|| Finally, let us learn how to extract a particular entry from some '''column''' of a '''data frame'''. 

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|| We will extract the third value in the fourth '''column''' of the '''captaincy data frame'''.

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|| Click on the '''script mydataframe.R'''.

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|| In the '''Source '''window, type '''captaincy '''within double square brackets '''4''' within single square brackets '''3'''. 

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|| Save the '''script''' and execute the current line. 

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|| The expected value''' 14''' is seen in the '''Console''' window.

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|| 11:48
|| For more information on '''indexing '''and '''slicing '''data frames, please refer to the '''Additional materials''' section on this website.

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

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|| In this tutorial, we have learnt how to:

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|| Extract rows or columns from a '''data frame'''

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|| 12:12
|| Create a '''subset''' from a '''data frame '''

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|| 12:16
|| Retrieve data using double square brackets 

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|| We now suggest an assignment.

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|| Create a '''subset '''from '''captaincy data frame''' with the captains who have played more than(>) 20 matches and lost less than(<) 14 matches. 


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|| 12:36
|| The video at the following link summarises the Spoken Tutorial project.

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|| 12:41
|| Please download and watch it.

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|| 12:44
|| We conduct workshops using Spoken Tutorials and give Certificates.

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|| 12:50
|| Please contact us.

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|| 12:53
|| Please post your timed queries in this forum.

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|| 12:57 
|| Please post your general queries in this forum.

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|| 13:02
|| The '''FOSSEE '''team coordinates the '''TBC '''project.

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|| 13:06
|| For more details, please visit these sites.

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|| 13:10
|| The Spoken Tutorial project is funded by NMEICT, MHRD, Govt. of India

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|| 13:16
|| The script for this tutorial was contributed by Shaik Sameer (FOSSEE Fellow 2018).

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|| 13:24
|| This is Sudhakar Kumar from IIT Bombay signing off. Thanks for watching.