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R While Loop


Loops

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.

R has two loop commands:

  • while loops
  • for loops

R While Loops

With the while loop we can execute a set of statements as long as a condition is TRUE:

Example

Print i as long as i is less than 6:

i <- 1
while (i < 6) {
  print(i)
  i <- i + 1
}
Try it Yourself »

In the example above, the loop will continue to produce numbers ranging from 1 to 5. The loop will stop at 6 because 6 < 6 is FALSE.

The while loop requires relevant variables to be ready, in this example we need to define an indexing variable, i, which we set to 1.

Note: remember to increment i, or else the loop will continue forever.


Break

With the break statement, we can stop the loop even if the while condition is TRUE:

Example

Exit the loop if i is equal to 4.

i <- 1
while (i < 6) {
  print(i)
  i <- i + 1
  if (i == 4) {
    break
  }
}
Try it Yourself »

The loop will stop at 3 because we have chosen to finish the loop by using the break statement when i is equal to 4 (i == 4).


Next

With the next statement, we can skip an iteration without terminating the loop:

Example

Skip the value of 3:

i <- 0
while (i < 6) {
  i <- i + 1
  if (i == 3) {
    next
  }
  print(i)
}
Try it Yourself »

When the loop passes the value 3, it will skip it and continue to loop.


Yahtzee!

If .. Else Combined with a While Loop

To demonstrate a practical example, let us say we play a game of Yahtzee!

Example

Print "Yahtzee!" If the dice number is 6:

dice <- 1
while (dice <= 6) {
  if (dice < 6) {
    print("No Yahtzee")
  } else {
    print("Yahtzee!")
  }
  dice <- dice + 1
}
Try it Yourself »

If the loop passes the values ranging from 1 to 5, it prints "No Yahtzee". Whenever it passes the value 6, it prints "Yahtzee!".