R While Loop
The while loop repeats a block of statements for as long as a given condition stays true, which makes it the right tool when you don't know in advance exactly how many times you need to repeat something.
The basic syntax
A while loop starts with the keyword while, followed by a condition in parentheses, followed by the body of the loop wrapped in curly braces. Before every single pass through the body, R checks the condition. If it evaluates to TRUE, the body runs and then R checks the condition again. As soon as the condition evaluates to FALSE, the loop stops and R moves on to the code that follows it.
Example
count <- 1
while (count <= 5) {
print(count)
count <- count + 1
}In this example, count starts at 1. Each time through the loop, R prints the current value and then increases count by one. Once count reaches 6, the condition count <= 5 becomes FALSE, so the loop stops, having printed the numbers 1 through 5.
Avoiding infinite loops
for loops are great when you already know how many times to repeat something, but a while loop shines when the number of repetitions depends on the data itself, such as when you keep transforming a value until it crosses some threshold.
Halving Example
value <- 100
steps <- 0
while (value >= 1) {
value <- value / 2
steps <- steps + 1
}
cat("It took", steps, "halvings to get below 1\n")- Repeating a calculation until the result is 'close enough' to a target value
- Simulating a process, such as compound interest, until a balance passes a goal
- Retrying an action until it succeeds or a maximum attempt count is reached
- Processing values one at a time until a stop signal appears in the data
Combining multiple conditions
Combined Condition
balance <- 1000
years <- 0
while (balance < 2000 && years < 50) {
balance <- balance * 1.05
years <- years + 1
}
cat("Balance passed 2000 after", years, "years\n")
