while loop

While Loop in R Programming

A While loop in R programming is a statement that keeps running until a condition after while block is satisfied.

While loop in R programming language is used when the exact number of iterations of loop is not known beforehand. It executes the same code again and again until a stop condition is met. While loop checks for the condition to be true or false n+1 times rather than n times. This is because the while loop checks for the condition before entering the body of the loop.

R- While loop Syntax: 

while (test_expression) {
   statement
   update_expression
}  

How does a While loop execute?  

• Control falls into the while loop.
• The flow jumps to Condition
• Condition is tested. 
  • If Condition yields true, the flow goes into the Body.
  • If Condition yields false, the flow goes outside the loop
• The statements inside the body of the loop get executed.
• Updation takes place.
• Control flows back to Step 2.
• The while loop has ended and the flow has gone outside.

Important Points about while loop in R language:  

• It seems to be that while loop will run forever but it is not true, condition is provided to stop it.
• When the condition is tested and the result is false then loop is terminated.
• And when the tested result is True, then loop will continue its execution.

R – while loop Flowchart: 

While Loop in R Programming Examples

Example 1: 

R

# R program to illustrate while loop   result <- c("Hello World") i <- 1   # test expression while (i < 6) {      print(result)         # update expression    i = i + 1 }

Output: 

[1] "Hello World"
[1] "Hello World"
[1] "Hello World"
[1] "Hello World"
[1] "Hello World"

Example 2:  

R

# R program to illustrate while loop   result <- 1 i <- 1   # test expression while (i < 6) {      print(result)         # update expression    i = i + 1    result = result + 1 }

Output: 

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5

R – while loop break

Here we will use the break statement in the R programming language. Break statement in R is used to bring the control out of the loop when some external

condition is triggered.

R

# R program to illustrate while loop   result <- c("Hello World") i <- 1   # test expression while (i < 6) {       print(result)           if( i == 3){         break}     # update expression     i = i + 1 }

Output:

[1] "Hello World"
[1] "Hello World"
[1] "Hello World

While Loop Syntax in R

Following is the syntax for While Loop in R programming:

while (condition) {
     Exp	
}

R While Loop Flowchart

R While Loop Flowchart

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

While Loop in R Programming Examples

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:
## 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

2. Example of while Loop
i <- 1

while (i < 6) {
   print(i)
   i = i+1
}
Output
[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
In the above example, i is initially initialized to 1.
Here, the test_expression is i < 6 which evaluates to TRUE since 1 is less than 6. So, the body of the loop is entered and i is printed and incremented.
Incrementing i is important as this will eventually meet the exit condition. Failing to do so will result into an infinite loop.
In the next iteration, the value of i is 2 and the loop continues.
This will continue until i takes the value 6. The condition 6 < 6 will give FALSE and the while loop finally exits.