View source for R/C2/Conditional-Statements/English

'''Title of the script''': Conditional Statements 

'''Author''': Varshit Dubey (CoE Pune) and Sudhakar Kumar (IIT Bombay)

'''Keywords''': R, RStudio, conditional, if, else, else if, video tutorial

{| border =1
|'''Visual Cue'''
|'''Narration'''
|-
|| Show slide 

Opening Slide
|| Welcome to this tutorial on '''Conditional Statements'''. 
|-
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Learning Objective

|| In this tutorial, we will learn about,
* Conditional statements
* '''if, else, '''and '''else if '''statements

|-
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Pre-requisites

[https://spoken-tutorial.org/ https://spoken-tutorial.org/]
|| To understand this tutorial, you should know, 
* Basic data structures 
* Indexing and slicing data frames 

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

System Specifications
|| This tutorial is recorded on
* '''Ubuntu Linux '''OS version '''16.04'''
* '''R''' version '''3.4.4'''
* '''RStudio''' version '''1.1.463'''

Install '''R''' version '''3.2.0''' or higher. 
|-
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Download Files
|| For this tutorial, we will use
* A '''data frame''' '''moviesData.csv'''
* A '''script''' file '''conditionalStats.R'''.

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

Highlight '''moviesData.csv '''and''' conditionalStats.R '''in the folder '''conditionalStatements'''
|| I have downloaded and moved these files to '''conditionalStatements''' folder. 

This folder is located in '''myProject''' folder on my '''Desktop'''.

I have also set '''conditionalStatements''' folder as my '''Working Directory.''' 
|-
|| Show slide 

Conditional Statements 
|| 
* Conditional statements are used to execute some logical conditions in the code.
* '''if''', '''else '''and '''else if '''are the basic conditional statements. 

|-
|| 
|| Let us switch to '''RStudio'''.
|-
|| Highlight '''conditionalStats.R''' in the '''Files '''window''' '''of '''RStudio '''
|| Open the '''script conditionalStats.R '''in''' RStudio'''. 
|-
|| Highlight''' inScore''' in the '''Source''' window 
|| Here, we have declared a vector''' inScore'''. 

The elements of this vector represent the runs scored by '''India''' in three different one-day matches. 
|-
|| Highlight''' ausScore''' in the '''Source''' window 
|| Similarly, we have declared another vector''' ausScore'''. 

The elements of this vector represent the runs scored by '''Australia''' in three different one-day matches. 
|-
|| Highlight the '''Source''' button
|| Run this '''script''' by clicking on the '''Source''' button. 
|-
|| Highlight '''movies''' in the '''Source''' window 
|| '''movies data frame''' opens in the '''Source''' window. 

This '''data frame''' will be used later in this tutorial. 
|-
|| Highlight the '''script conditionalStats.R''' in the '''Source''' window 
|| Click on the '''script conditionalStats.R'''
|-
|| Highlight''' inScore''' and '''ausScore''' in the '''Source''' window 
|| Let us now find which country has won the first one day match. 

|-
|| [RStudio]

'''if(inScore[1] > ausScore[1]){'''

'''print("India won the first ODI!")'''

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

|-
|| Highlight '''if''' in the '''Source''' window 
|| It means that '''if''' the '''condition '''is '''TRUE '''then execute the '''expression''' inside the curly brackets.
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line by pressing '''Ctrl+Enter''' keys simultaneously. 
|-
|| 
|| I will resize the '''Console''' window. 
|-
|| Highlight the output in the '''Console''' window 
|| As '''India''' scored more runs than '''Australia''' in the first one day match, the message,  '''India won the first ODI!, ''' is displayed.
|-
|| Highlight''' inScore''' and '''ausScore''' in the '''Source''' window 
|| Let us now find which country won the second one day match. 
|-
|| 
|| I will resize the '''Console''' window. 
|-
|| [RStudio]

'''if (inScore[2] > ausScore[2]){'''

'''print("India won the second ODI!")'''

'''}'''
|| In the '''Source''' window, type the following command. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line. 
|-
|| Highlight''' inScore''' and '''ausScore''' in the '''Source''' window.

Highlight the output in the '''Console''' window
|| As Australia scored more runs than India in the second one day match, we should get a message, '''Australia won the second ODI!.'''

But no message is displayed on the '''Console.'''
|-
|| Highlight the last '''if''' statement in the '''Source''' window 
|| Here the '''if''' statement will be executed only when '''India''' scores more runs than '''Australia''' in the second one day match. 

Hence, we need to add an '''else''' statement with another expression. 

This expression should be executed when the '''if''' condition is not satisfied. 
|-
|| Highlight the last '''if''' statement in the '''Source''' window 
|| Click on the last line of the '''if '''statement. 
|-
|| [RStudio]

'''else{'''

'''print("Australia won the second ODI!")'''

'''}'''
|| Now, type the following command. 

Please note that the '''else''' statement begins on the same line where '''if''' statement ends. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line. 
|-
|| 
|| I will resize the '''Console''' window. 
|-
|| Highlight the output in the '''Console''' window 
|| Now, we get a message,  '''Australia won the second ODI!'''
|-
|| Highlight the '''if-else''' statement in '''Source''' window 
|| There is another efficient way to write this '''if-else''' statement. 
|-
|| [RStudio]

'''ifelse (inScore[2] > ausScore[2], '''

'''"India won the second ODI!",'''

'''"Australia won the second ODI!")'''
|| In the '''Source''' window, type the following command. 
|-
|| Highlight '''ifelse''' in the '''Source''' window
|| Here, we are using '''ifelse''' for comparing the elements of two different vectors. 
|-
|| Highlight '''ifelse''' in the '''Source''' window

Highlight '''inScore[2] > ausScore[2] '''in the '''Source''' window
|| Here the '''ifelse''' statement has three arguments.

* '''test''' - It is an object which can be forced to a logical mode. 

Here '''test '''is for the comparison of scores. 
|-
|| Highlight '''India won the second ODI! '''in the '''Source''' window
|| 
* '''yes''' - It returns values for true elements of the '''test.'''

Here, the first statement represents the value of the true element. 
|-
|| Highlight '''Australia won the second ODI! '''in the Source window 
|| 
* '''no''' - It returns values for false elements of the '''test''' 

The second statement represents the value of the false element. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line. 
|-
|| Highlight the output in the '''Console''' window 
|| We get the same message,  '''Australia won the second ODI!'''

In the  '''Source'''  window, scroll up to locate the two vectors.
|-
| | Highlight''' inScore''' and '''ausScore''' in the '''Source''' window 
| | In the third one day match, '''India''' and '''Australia''' have scored the same number of runs. 

Let us use an '''if-else''' logic to find out the winner in this case. 
|-
| | [RStudio]

'''if (inScore[3] > ausScore[3]){'''

'''print("India won the third ODI!")'''

'''} else{'''

'''print("Australia won the third ODI!")'''

'''}'''
| | In the '''Source''' window, click on the next line after the ifelse statement. 

Now type the following command. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line. 
|-
|| Highlight the output in the '''Console''' window 
|| We get the message,  '''Australia won the third ODI! ''' This is not correct. 
|-
|| Highlight the '''if-else''' statement in the Source window 
|| So, we need to modify our logic. 
|-
| | [RStudio]

'''if (inScore[3] > ausScore[3]){'''

'''print("India won the third ODI!")'''

'''} else if (inScore[3] == ausScore[3]){'''

'''print("Third ODI was a tie.")'''

'''} else {'''

'''print("Australia won the third ODI!")'''

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


Please note that '''else''' '''if''' statement begins on the same line where '''if''' statement ends. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Run the current line. 
|-
|| 
|| I will resize the '''Console''' window. 
|-
|| Highlight the output in the '''Console''' window 
|| Now, we got the correct message,  '''Third ODI was a tie. '''
|-
|| 
|| I will resize the '''Console''' window again. 
|-
|| Highlight the last if-else statement in the '''Source''' window 
|| A conditional structure contains, only one '''if '''statement.

It may contain as many '''else if '''statements''' '''as you need and only one '''else '''statement.

The '''else '''statement will be executed only when all the above '''if '''and '''else if''' statements are '''FALSE'''. 
|-
|| Highlight '''ifelse''' statement in the Source window 
|| In the '''Source''' window, scroll up. 

Here, we have used '''ifelse''' for comparing the elements of two different vectors. 
|-
|| Highlight '''ifelse''' in the '''Source''' window
|| Now, we will learn how to use '''ifelse''' statements for comparing the two columns of a '''data frame'''. 
|-
|| Highlight '''movies''' in the '''Source''' window 
|| In the '''Source''' window, scroll down to locate the last if-else statement. 

In the '''Source''' window, click on '''movies data frame. '''
|-
|| Highlight the scroll bar in the '''Source''' window 
|| In the '''Source''' window, scroll from left to right. 

This will enable us to see the remaining objects of '''movies''' '''data frame'''. 
|-
|| Highlight '''audience_score''' and '''critics_score''' in '''movies''' 
|| Let us compare the '''critics_score '''and '''audience_score''' . 

We will add a new column named '''dev''' in the '''movies data frame''', which will show 
* 1, if '''audience_score '''is greater than '''critics_score'''
* 0,''' '''otherwise'''. '''

|-
|| Highlight the '''script conditionalStats.R''' in the '''Source''' window 
|| Click on the '''script conditionalStats.R'''
|-
|| [RStudio]

'''movies$dev <- ifelse(movies$audience_score > movies$critics_score, 1, 0)'''

'''View(movies)'''
|| In the '''Source''' window, type the following command. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the last two lines. 
|-
|| Highlight '''movies''' in the '''Source''' window 
|| '''movies data frame''' opens in the '''Source''' window. 
|-
|| Highlight the scroll bar in the '''Source''' window 
|| In the '''Source''' window, scroll from left to right. 
|-
|| Highlight '''dev''' in '''movies''' 
|| A new column named '''dev''' has been added. It has 1 or 0. 

Remember, 1 means '''audience_score''' is greater than '''critics_score'''. 

Now, we will find the number of '''movies''', in which '''audience_score '''is greater than '''critics_score'''. 

For this, we will use the '''sum''' function along with the '''if''' condition.
|-
|| Highlight the '''script conditionalStats.R''' in the '''Source''' window 
|| Click on the '''script conditionalStats.R'''
|-
|| [RStudio]

'''sum(ifelse(movies$audience_score > movies$critics_score, 1, 0))'''
|| In the '''Source''' window, type the following command. 
|-
|| Highlight '''Run''' button in the '''Source''' window 
|| Save the '''script''' and run the current line. 
|-
|| Highlight the output in the Console window 
|| So, there are 312 movies, in which '''audience_score '''is greater than '''critics_score'''. 
|-
|| 
|| Let us summarize what we have learnt.
|-
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Summary
|| In this tutorial, we have learnt about,
* Conditional statements
* '''if, else, '''and '''else if '''statements

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Assignment
|| We now suggest an assignment.
* Use the built-in data set  '''iris'''. Find the '''Species''', in which '''Sepal.Length''' is greater than '''Petal.Length'''
* Count all such '''Species'''. 

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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.
|-
|| Show slide

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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Acknowledgment
|| 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 Varshit Dubey (College of Engineering Pune).

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