R - While Loop

A loop statement allows a program to execute a given block of codes repeatedly under a given condition. This enables a programmer to write programs in fewer lines of code and enhance the code readability. R has following types of loop to handle the looping requirements:

while loop
for loop
repeat loop

The While Loop

The While loop allows a set of statements to be executed repeatedly as long as a specified condition is true. It can be viewed as a repeating if statement. A while loop is preferred over for loop whenever number of iteration is not known beforehand.

Syntax

while (condition) {
  statements
}

Flow Diagram:

In below mentioned example, program uses while loop to sum all integers from 1 to 5.

sum <- 0
i <- 1
while (i < 6){
  sum <- sum + i
  i <- i+1
}
print(sum)

The output of the above code will be:

[1] 15

next statement

By using next statement, the program skips the loop whenever condition is met, and brings the program to the start of loop. Please consider the example below.

i <- 1

#skips the loop for odd value of i
while (i <= 10) {
  if(i %% 2 == 1) {
    i <- i + 1
    next
  }
  print(i)
  i <- i + 1
}

The output of the above code will be:

[1] 2
[1] 4
[1] 6
[1] 8
[1] 10

break statement

By using break statement, the program get out of the for loop when condition is met. Please consider the example below.

i <- 1

#get out of the loop when i == 5
while (i <= 10) {
  if(i == 5) 
    break
  print(i)
  i <- i + 1
}

The output of the above code will be:

[1] 1
[1] 2
[1] 3
[1] 4