Lære Repeat Loops and Break Statements

When you need to repeat a block of code an unknown number of times until a specific condition is met, you can use a repeat loop in R. Unlike for or while loops, a repeat loop does not check a condition at the start or end of each iteration. Instead, it will continue executing indefinitely until you explicitly tell it to stop, making it useful for cases where the number of iterations is not known in advance.


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# Print numbers 1 to 5 using a repeat loop and break
i <- 1
repeat {
  print(i)
  i <- i + 1
  if (i > 5) {
    break
  }
}

In this example, the repeat loop starts with i equal to 1 and prints the value of i in each iteration. After printing, i is incremented by 1. The if statement checks if i is greater than 5, and if so, the break statement is used to exit the loop. Without the break, the loop would run forever. This demonstrates that a repeat loop always relies on an explicit break to stop execution.

Definition

The break statement in R is used to immediately exit a loop, regardless of the loop's original stopping condition. It is especially important in repeat loops, where there is no automatic condition to stop the loop.


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# Repeat loop: generate random numbers until one is greater than 0.9
count <- 0
repeat {
  num <- runif(1)
  count <- count + 1
  print(num)
  if (num > 0.9) {
    print(paste("Stopped after", count, "tries."))
    break
  }
}

This pattern is useful when you want to run a simulation or wait for a random event, such as generating random numbers until one meets a certain threshold. The repeat loop continues generating and printing random numbers, and only exits when the generated number is greater than 0.9, thanks to the break statement.


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# Example of a repeat loop without a break (do not run!)
repeat {
  print("This will run forever!")
}

If you omit the break statement in a repeat loop, the loop will never stop on its own. This results in an infinite loop, which can freeze or crash your R session. Always make sure your repeat loops have a reliable way to exit. As a best practice, use repeat loops only when you cannot determine the number of iterations in advance, and always include a clear condition that leads to a break.

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Sektion 2. Kapitel 5

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Suggested prompts:

Can you explain the difference between repeat, while, and for loops in R?

What are some common use cases for repeat loops?

How can I avoid creating infinite loops when using repeat in R?

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              123456789
            
# Print numbers 1 to 5 using a repeat loop and break
i <- 1
repeat {
  print(i)
  i <- i + 1
  if (i > 5) {
    break
  }
}

Definition


              1234567891011
            
# Repeat loop: generate random numbers until one is greater than 0.9
count <- 0
repeat {
  num <- runif(1)
  count <- count + 1
  print(num)
  if (num > 0.9) {
    print(paste("Stopped after", count, "tries."))
    break
  }
}


              1234
            
# Example of a repeat loop without a break (do not run!)
repeat {
  print("This will run forever!")
}

Var alt klart?

Tak for dine kommentarer!

Sektion 2. Kapitel 5

Repeat Loops and Break Statements

1. What is the main difference between repeat and while loops?

2. How does the break statement work in R loops?

3. Why is it important to include a break in a repeat loop?

Repeat Loops and Break Statements

1. What is the main difference between repeat and while loops?

2. How does the break statement work in R loops?

3. Why is it important to include a break in a repeat loop?