While Loop in R with Example

A loop is a statement that keeps running until a condition is satisfied. The syntax for a while loop is the following:

while (condition) { Exp }

While Loop Flow Chart

Note : Remember to write a closing condition at some point otherwise the loop will go on indefinitely.

Example 1:

Let’s go through a very simple example to understand the concept of while loop. You will create a loop and after each run add 1 to the stored variable. You need to close the loop, therefore we explicitely tells R to stop looping when the variable reached 10.

Note : If you want to see current loop value, you need to wrap the variable inside the function print().

#Create a variable with value 1 begin <- 1 #Create the loop while (begin <= 10){ #See which we are cat(‘This is loop number’,begin) #add 1 to the variable begin after each loop begin <- begin+1 print(begin) }

Output:

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This is loop number 1[1] 2 ## This is loop number 2[1] 3 ## This is loop number 3[1] 4 ## This is loop number 4[1] 5 ## This is loop number 5[1] 6 ## This is loop number 6[1] 7 ## This is loop number 7[1] 8 ## This is loop number 8[1] 9 ## This is loop number 9[1] 10 ## This is loop number 10[1] 11

Example 2:

You bought a stock at price of 50 dollars. If the price goes below 45, we want to short it. Otherwise, we keep it in our portfolio. The price can fluctuate between -10 to +10 around 50 after each loop. You can write the code as follow:

set.seed(123) # Set variable stock and price stock <- 50 price <- 50 # Loop variable counts the number of loops loop <- 1 # Set the while statement while (price > 45){ # Create a random price between 40 and 60 price <- stock + sample(-10:10, 1) # Count the number of loop loop = loop +1 # Print the number of loop print(loop) }

Output:

[1] 2 ## [1] 3 ## [1] 4 ## [1] 5 ## [1] 6 ## [1] 7

cat(‘it took’,loop,‘loop before we short the price. The lowest price is’,price)

Output:

it took 7 loop before we short the price.The lowest price is 40