Difference between revisions of "R/C2/Conditional-Statements/English"

Opening Slide

Learning Objective

• Conditional statements
• if, else, and else if statements

Pre-requisites

https://spoken-tutorial.org/

• Basic data structures
• Indexing and slicing data frames

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

System Specifications

• Ubuntu Linux OS version 16.04
• R version 3.4.4
• RStudio version 1.1.463

Install R version 3.2.0 or higher.

Download Files

• A data frame moviesData.csv
• A script file conditionalStats.R.

Please download these files from the Code files link of this tutorial.

Highlight moviesData.csv and conditionalStats.R in the folder conditionalStatements

This folder is located in myProject folder on my Desktop.

I have also set conditionalStatements folder as my Working Directory.

Conditional Statements

• Conditional statements are used to execute some logical conditions in the code.
• if, else and else if are the basic conditional statements.

The elements of this vector represent the runs scored by India in three different one-day matches.

The elements of this vector represent the runs scored by Australia in three different one-day matches.

This data frame will be used later in this tutorial.

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

print("India won the first ODI!")

}

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

print("India won the second ODI!")

}

Highlight the output in the Console window

But no message is displayed on the Console.

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

This expression should be executed when the if condition is not satisfied.

else{

print("Australia won the second ODI!")

}

Please note that the else statement begins on the same line where if statement ends.

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

"India won the second ODI!",

"Australia won the second ODI!")

Highlight inScore[2] > ausScore[2] in the Source window

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

Here test is for the comparison of scores.

• yes - It returns values for true elements of the test.

Here, the first statement represents the value of the true element.

• no - It returns values for false elements of the test

The second statement represents the value of the false element.

In the Source window, scroll up to locate the two vectors.

Let us use an if-else logic to find out the winner in this case.

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

print("India won the third ODI!")

} else{

print("Australia won the third ODI!")

}

Now type the following command.

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!")

}

Please note that else if statement begins on the same line where if statement ends.

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.

Here, we have used ifelse for comparing the elements of two different vectors.

In the Source window, click on movies data frame.

This will enable us to see the remaining objects of movies data frame.

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.

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

View(movies)

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.

sum(ifelse(movies$audience_score > movies$critics_score, 1, 0))

Summary

• Conditional statements
• if, else, and else if statements

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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Acknowledgment

Thank You

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