R - while loop - GeeksforGeeks

R – while loop

Last Updated : 21 Apr, 2020

While loop in R is used when the exact number of iterations of loop is not known beforehand. It executes the same code again and again until a stop condition is met.

while loop checks for the condition to be true or false n+1 times rather than n times. This is because while loop checks for the condition before entering the body of the loop.

Syntax:

while (test_expression) {
   statement
   update_expression
}

While-loop-in-R

How does a While loop execute?

Control falls into the while loop.
The flow jumps to Condition
Condition is tested.
1. If Condition yields true, the flow goes into the Body.
2. If Condition yields false, the flow goes outside the loop
The statements inside the body of the loop get executed.
Updation takes place.
Control flows back to Step 2.
The while loop has ended and the flow has gone outside.

Important Points about while loop:

It seems to be that while loop will run forever but it is not true, condition is provided to stop it.
When the condition is tested and the result is false then loop is terminated.
And when the tested result is True, then loop will continue its execution.

Flowchart:
while-loop-flowchart-in-R

Example 1:

# R program to illustrate while loop
  
result <- c("Hello World")
i <- 1
  
# test expression 
while (i < 6) {
  
   print(result)
     
   # update expression 
   i = i + 1
}

Output:

[1] "Hello World"
[1] "Hello World"
[1] "Hello World"
[1] "Hello World"
[1] "Hello World"

Example 2:

# R program to illustrate while loop
  
result <- 1
i <- 1
  
# test expression 
while (i < 6) {
  
   print(result)
     
   # update expression 
   i = i + 1
   result = result + 1
}

Output:

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

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