If-Else Statement in R

In this tutorial, we will learn about if-else statements in R. We will cover the basics of conditional execution using if-else statements.

What is an If-Else statement

An if-else statement is a conditional statement that executes one block of code if a specified condition is true, and another block of code if the condition is false.

Syntax

The syntax for the if-else statement in R is:

if (condition) {
    # Code block to execute if condition is true
} else {
    # Code block to execute if condition is false
}

The if-else statement evaluates the specified condition. If the condition is true, the code block inside the if statement is executed; otherwise, the code block inside the else statement is executed.

Flowchart of If Else Statement

Example 1: Checking if a Number is Even or Odd

In R, checking if a number is even or odd within an if-else statement involves using the modulo operator (%) to determine if the remainder when dividing by 2 is zero. If it's zero, the number is even; otherwise, it's odd.

For example,

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is even or odd.
  4. Print a message indicating whether num is even or odd.

R Program

num <- 10
if (num %% 2 == 0) {
    print(paste(num, 'is even.'))
} else {
    print(paste(num, 'is odd.'))
}

Output

10 is even.

Example 2: Checking if a String Starts with a Specific Value

In R, checking if a string starts with a specific value can be achieved using the `startsWith()` function from the `stringr` package or regular expressions with functions like `grepl()` within an if statement.

For example,

  1. Declare a variable str.
  2. Assign a value to str.
  3. Use an if-else statement to check if str starts with a specific value.
  4. Print a message indicating the result of the check.

R Program

str <- 'Hello, world!'
if (grepl('^Hello', str)) {
    print('String starts with 'Hello'.')
} else {
    print('String does not start with 'Hello'.')
}

Output

String starts with 'Hello'.

Example 3: Checking if a Number is Positive or Negative

In R, checking if a number is positive or negative within an if-else statement involves evaluating the number's sign using conditions like greater than zero (>0) for positive numbers, less than zero (<0) for negative numbers, and equal to zero (==0) for zero.

For example,

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is positive or negative.
  4. Print a message indicating whether num is positive or negative.

R Program

num <- -5
if (num > 0) {
    print(paste(num, 'is positive.'))
} else {
    print(paste(num, 'is negative or zero.'))
}

Output

-5 is negative or zero.