What are the loop commands in R?

Overview

A loop in programming is a sequence of instructions that is continually repeated until a certain condition is reached. Loops continue to execute a block of code until the given condition is achieved.

Loop commands in R

In R language, there are two types of loop commands:

  • The while loop command
  • The for loop command

The while loop command

The while loop will execute a set of statements as long as the given condition is true.

Syntax of the while loop

While(expression){
  statement(s)
}

The statement provided will continue to be executed in the code snippet above if the expression or condition provided is TRUE.

Example

In the code below, we want to print the values of the variable x as long as x is less than 5.

Note: The expression or the condition given here can be read as "as long as x is less than 5"

# creating a variable
x <- 1
# using the while loop
while (x < 5) {
# printing the statement to be executed
  print(x)
  x <- x + 1
}

Explanation

In the example above, x has an initial value of 1 and will be incremented by 1 after each iteration of the loop. The output should produce a sequence of numbers starting from 1 to 4, and the terminating condition for the loop will be x < 5.

The while loop requires relevant variables to be ready. In the code above, we needed to define an indexing variable, x, which we set to 1.

The for loop command

A for loop command in R is used to iterate over a sequence.

Syntax of the for loop

for(expression){
  statement(s)
}

Example

In the code below, we want to print the values of x within the range 1 to 10.

for (x in 1:10) {
  print(x)
}

In the code above, we print the values of x between the range 1 to 10 using the for loop.

We can also see that the for loop here is more like an iterator method that loops through a collection of items one at a time, which is normally seen in other programming languages as well.

Note: This is a bit different from a simple for loop.

Summary

The only difference between for and while loop commands is that the former (for loop) does not require an indexing variable to be set beforehand while the latter (while loop) does.

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