Apprendre While Loops in R | R Loops Tutorial

While loops in R are a fundamental control flow tool, especially useful when you do not know in advance how many times you need to repeat a block of code. Unlike for loops, which iterate over a known sequence or range, a while loop keeps running as long as a specified condition remains true. This makes while loops ideal for tasks such as:

Waiting for a certain value to be reached;
Searching through data until a match is found;
Performing calculations that depend on dynamic criteria.

Use while loops when you need flexibility and do not have a fixed number of iterations.


              123456
            
# Print numbers from 1 to 5 using a while loop
i <- 1
while (i <= 5) {
  print(i)
  i <- i + 1
}

In the while loop above, you start by initializing a loop variable, i, to 1. The loop condition, i <= 5, is checked before each iteration. As long as this condition is true, the code inside the loop runs. After printing the current value of i, you update i by adding 1. This update is essential; without it, the loop condition would never change, and the loop would run forever.

Definition

The loop condition is the logical expression tested before each iteration of a loop. It determines whether the loop should continue or stop. If the condition never becomes FALSE, the loop will not terminate on its own.


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# Find the first number greater than 100 in a vector using a while loop
numbers <- c(10, 25, 99, 105, 42)
i <- 1
while (i <= length(numbers) && numbers[i] <= 100) {
  i <- i + 1
}
if (i <= length(numbers)) {
  print(numbers[i])
} else {
  print("No number greater than 100 found.")
}

This example demonstrates using a while loop to search for the first number greater than 100 in a vector. You start at the first element and continue looping as long as you have not reached the end of the vector and the current number is not greater than 100. The loop variable, i, is updated in every iteration to move to the next element. Properly updating the loop variable is crucial—if you forget to do so, the loop may never end.


              1234
            
# Infinite while loop (for demonstration; do not run!)
while (TRUE) {
  print("This will run forever!")
}

To avoid infinite loops, always make sure that something inside the loop will eventually make the loop condition false. This usually means updating a variable that is part of the condition. Double-check your loop logic and test with small examples to ensure the loop stops as expected.

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Section 2. Chapitre 3

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Waiting for a certain value to be reached;
Searching through data until a match is found;
Performing calculations that depend on dynamic criteria.

Use while loops when you need flexibility and do not have a fixed number of iterations.


              123456
            
# Print numbers from 1 to 5 using a while loop
i <- 1
while (i <= 5) {
  print(i)
  i <- i + 1
}

Definition


              1234567891011
            
# Find the first number greater than 100 in a vector using a while loop
numbers <- c(10, 25, 99, 105, 42)
i <- 1
while (i <= length(numbers) && numbers[i] <= 100) {
  i <- i + 1
}
if (i <= length(numbers)) {
  print(numbers[i])
} else {
  print("No number greater than 100 found.")
}


              1234
            
# Infinite while loop (for demonstration; do not run!)
while (TRUE) {
  print("This will run forever!")
}

Tout était clair ?

Merci pour vos commentaires !

Section 2. Chapitre 3

While Loops in R

1. When would you use a while loop instead of a for loop?

2. What is a potential risk when using while loops?

3. How can you ensure a while loop eventually stops?

While Loops in R

1. When would you use a while loop instead of a for loop?

2. What is a potential risk when using while loops?

3. How can you ensure a while loop eventually stops?