R if Statement

The if statement is a conditional statement that allows you to provide conditions to execute a piece of code.

The syntax of if statement in R is:

if(test_expression) {
  # body of if statement
}

If the test_expression inside the if statement is TRUE, then the code inside the if block will be executed.

else Statement

You can use the else statement along with an if statement to specify code to be executed if the test_expression in if statement returns FALSE.

if(test_expression) {
  # block of code if condition is true
} else {
  # block of code if condition is false
}

Example 1: R if…else Statement

x <- 12

# check if x is positive or negative number
if (x > 0) {
  print("x is a positive number")
} else {
  print("x is a negative number")
}

Output

[1] "x is a positive number"

Here, since x > 0 evaluates to TRUE, the code inside the if block gets executed.

The if…else if…else Statement

If you want to test more than one condition, you can use the optional else if statement along with your if...else statements. The syntax is:

if(test_expression_1) {
  # code block 1
} else if (test_expression_2){
  # code block 2
} else {
  # code block 3
}

Here,

• if test_expression_1 returns TRUE, then code block 1 is executed.
• if test_expression_1 returns FALSE, then the test_expression_2 is evaluated.
• if test_expression_2 returns TRUE, then the code block 2 is executed.
• if test_expression_2 returns FALSE, then code block 3 is executed.

Example 2: R if…else if…else Statement

x <- 0

# check if x is positive or negative or zero
if (x > 0) {
  print("x is a positive number")
} else if (x < 0) {
  print("x is a negative number")
} else {
  print("x is zero")
}

Output

[1] "x is zero"

In this program, we have used an if...else if...else block to check whether x is a positive number, a negative number, or zero. Here,

• if (x > 0) {...} is executed if x is positive
• else if (x < 0) {...} is executed if x is negative
• else {...} is executed if x is 0

Since x = 0, the else block is executed.

Nested if...else Statements

You can have nested if...else statements inside if...else blocks in R. This allows you to specify conditions inside conditions. For example,

x <- 20

# check if x is positive
if (x > 0) {

  # check if x is even or odd
  if (x %% 2 == 0) {
    print("x is a positive even number")
  } else {
    print("x is a positive odd number")
  }

# execute if x is not positive
} else {

  # check if x is even or odd
  if (x %% 2 == 0) {
    print("x is a negative even number")
  } else {
    print("x is a negative odd number")
  }
}

Output

[1] "x is a positive even number"

In this program,

• The outer if...else block checks whether x is positive or negative. If x is greater than 0, the code inside the outer if block is executed. Otherwise, the code inside the outer else block is executed.
  
  

  if (x > 0) {
    ... .. ...
  } else {
    ... .. ...
  }

• The inner if...else block checks whether x is even or odd. If x is perfectly divisible by 2, the code inside the inner if block is executed. Otherwise, the code inside the inner else block is executed.
  
  

  if (x %% 2 == 0) {
    ... .. ...
  } else {
    ... .. ...
  }