Introduction
In this article, we will learn about control structures in the R Programming Language. Control structures allow you to control the flow of execution of R statements. We will look at the if-else statement, for loops, nested loops, while loops, repeat loops, next, return and break statements etc. We will also look at examples for clear understanding. Let’s start the article.
Let us understand briefly what Control statements are.
Control Statements in R
What control statements are is quite evident by their name. Control statements are used to alter the flow of execution. It enables you to put some logic into your code. It helps reduce repetitive code. It allows the execution of lines of code based on certain conditions. It gives the programmer control over how many times a program line should be executed. Control structures are used in writing, functions or longer expressions.
If Statement
The ‘if’ control statement allows you to execute a code block if a given condition is true. When the condition is true, the code block is executed. When it is false, the code block is skipped.
Syntax
if(Condition){
statements
....
# code will be executed if the condition is true.
}
Let’s see an example of the same.
Code
weather <- "rainy"
if(weather == "rainy"){
print("Weather today is rainy")
}
Output
If-else Statement
The 'if-else' statement is the most commonly used in programming. It allows you to test a condition and act accordingly. It will enable the user to execute different statements based on whether the condition is true or false.
Syntax
if(Condition){
statements
....
# code will be executed if the condition is true.
}
else{
statements
....
# code will be executed if the condition is false.
}
Let’s see an example of the same.
Code
num1 = 20
num2 = 10
if (num1 > num2){
print("number 1 is greater than number 2")
}
else (val1 < val2){
print("number 1 is less than number 2")
}
Output
If-else if-else Statement
The ‘If-else if-else’ allows you to test multiple conditions. Once an if statement is true, the code for that statement will be executed. Rest all if conditions will be skipped. And if none of the if conditions is true, then the last else part will be executed.
Syntax
if(Condition 1){
statements
....
# code will be executed if condition1 is true.
}
else if(Condition 2){
statements
....
# code will be executed if condition 2 is true.
}
else {
statements
....
# code will be executed if all the if conditions are false.
}
Let’s see an example of the same.
Code
weather <-"rainy"
if(weather == "windy"){
print("Today weather is windy")
}
else if(weather == "rainy"){
print("Today weather is rainy!!")
}
else {
print("weather is as clear")
}
Output
For Loop
The ‘for’ loop allows you to iterate over a sequence. The loop continues until a specific condition is reached. It can iterate over objects for a fixed number of times.
Syntax
for(value in sequence){
statements
....
....
}
Let’s see an example of the same.
Code
list <- letters[0:5]
for(i in list){
print(i)
}
Output
Nested Loop
Nested loops are nothing but loops inside a loop. Nested loops are commonly used to iterate on matrices.
Syntax
for(value in sequence){
for(value in sequence){
statements
....
....
}
}
Let’s see an example of the same.
Code
mat <- matrix(2:10, 3)
for (r in seq(nrow(mat))) {
for (c in seq(ncol(mat))) {
print(mat[r, c])
}
}
Output
While Loop
The ‘while’ loop will keep running the code block as long as the condition remains true. First, it checks the condition. If the condition is true, it will execute the code block. Now it will recheck the condition. Thus, the loop keeps running until the condition turns out to be false.
Syntax
while(condition){
statement
....
# code will be executed if the condition is true.
}
Let’s see an example of the same.
Code
x = 1
while(x <= 5){
print(x)
x = x + 1
}
Output
Repeat loops
The ‘repeat’ loop is an infinite loop. We can exit this infinite loop by using the break statement. It can be used when the number of iterations is unknown. We can specify a condition when we want to end the loop. When the condition is true, we can call the break statement.
Syntax
repeat {
statements
....
if(condition) {
break
}
}
Let’s see an example of the same.
Code
x = 1
repeat{
print(x)
x = x + 1
if(x > 5){
break
}
}
Output
Next Statement
The ‘next’ statement skips the current iteration and moves to the next one. It does not terminate the loop. All the statements after the next statement will not be executed.
Let’s see an example of the same.
Code
# Defining vector
vec <- 1:5
# Print all numbers except 3
for(i in vec){
if(i == 3){
next #skips this iteration
}
print(i)
}
Output
Break Statement
The ‘break’ statement can be used to exit from the loop. It ends the loop and starts running the immediate next statement after the loop. It is commonly used with conditional statements to leave loops based on certain conditions.
Let’s see an example of the same.
Code
for (i in 1:10) {
# Print the current number
print(i)
# If the number is 5, break out of the loop
if (i == 5) {
break
}
}
print("the loop was terminated ")
Output
Return Statement
The return statement is used to exit a function. It can also return values when required. It immediately terminates the function when encountered.
Syntax
return(expression)
Let’s see an example of the same.
Code
evenodd <- function(x){
if(x %% 2 == 0){
return("Even")
}
else{
return("Odd")
}
}
evenodd(2)
evenodd(3)
Output
7+ registered 
