6.5 Using repeat loops to execute until told to break

A repeat loop is used to iterate over a block of code multiple number of times. There is test expression in a repeat loop to end or exit the loop. Rather, we must put a condition statement explicitly inside the body of the loop and use the break function to exit the loop. Failing to do so will result into an infinite loop.

# syntax of repeat loop
counter <- 1

repeat {
        statement
        
        if(test_expression){
                break
        }
        counter <- counter + 1
}

For example ,say we want to randomly draw values from a uniform distribution between 1 and 25. Furthermore, we want to continue to draw values randomly until our sample contains at least each integer value between 1 and 25; however, we do not care if we’ve drawn a particular value multiple times. The following code repeats the random draws of values between 1 and 25 (in which we round). We then include an if statement to check if all values between 1 and 25 are present in our sample. If so, we use the break statement to exit the loop. If not, we add to our counter and let the loop repeat until the conditional if statement is found to be true. We can then check the counter object to assess how many iterations were required to reach our conditional requirement.

counter <- 1
x <- NULL

repeat {
        x <- c(x, round(runif(1, min = 1, max = 25)))
        
        if(all(1:25 %in% x)){
                break
        }
                
        counter <- counter + 1
}

counter
[1] 75