if...else statement

Decision making is an important part of programming. This can be achieved in R programming using the conditional if...else statement.

if statement

Syntax of if statement

if (test_expression) {
   statement
}

If the test_expression is TRUE, the statement gets executed. But if it's FALSE, nothing happens. Here, test_expression can be a logical or numeric vector, but only the first element is taken into consideration. In the case of numeric vector, zero is taken as FALSE, rest as TRUE.

Flowchart of if statement

Example of if statement

x <- 5
if(x > 0){
   print("Positive number")
}

Output

[1] "Positive number"

if...else statement

Syntax of if...else statement

if (test_expression) {
   statement1
} else {
   statement2
}

The else part is optional and is evaluated if test_expression is FALSE. It is important to note that else must be in the same line as the closing braces of the if statements.

Flowchart of if...else statement

Example of if...else statement

x <- -5
if(x > 0){
   print("Non-negative number")
} else {
   print("Negative number")
}

 

Output

[1] "Negative number"

The above conditional can also be written in a single line as follows.

if(x > 0) print("Non-negative number") else print("Negative number")

This feature of R allows us to write construct as shown below.

> x <- -5
> y <- if(x > 0) 5 else 6
> y
[1] 6

Nested if...else statement

We can nest as many if...else statement as we want as follows.

Syntax of nested if...else statement

if ( test_expression1) {
   statement1
} else if ( test_expression2) {
   statement2
} else if ( test_expression3) {
   statement3
} else
   statement4

Only one statement will get executed depending upon the test_expressions.

Example of nested if...else statement

x <- 0
if (x < 0) {
   print("Negative number")
} else if (x > 0) {
   print("Positive number")
} else
   print("Zero")

Output

[1] "Zero"