Ifelse vectorized function in R Programming

Introduction

The ifelse function helps you quickly choose values from two options based on a condition for many items at once.

You want to label numbers as 'big' or 'small' depending on their size.

You need to replace missing values in a list with a default value.

You want to create a new list showing 'pass' or 'fail' based on scores.

You want to change colors in a list based on a condition.

Syntax

R Programming

ifelse(test_expression, yes, no)

test_expression is a condition checked for each item in a vector.

yes is the value chosen if the condition is TRUE; no is chosen if FALSE.

Examples

Checks each number in x; if greater than 10, returns 'big', else 'small'.

R Programming

x <- c(5, 10, 15)
ifelse(x > 10, "big", "small")

Labels scores 60 or above as 'pass', others as 'fail'.

R Programming

scores <- c(80, 55, 90)
ifelse(scores >= 60, "pass", "fail")

Replaces missing values (NA) with 0, keeps others unchanged.

R Programming

values <- c(NA, 2, NA, 4)
ifelse(is.na(values), 0, values)

Sample Program

This program labels each age as 'adult' if 18 or older, otherwise 'child'.

R Programming

ages <- c(12, 25, 17, 30)
labels <- ifelse(ages >= 18, "adult", "child")
print(labels)

Important Notes

ifelse works on whole vectors at once, so it is faster and simpler than writing loops.

The output vector has the same length as the input test_expression vector.

You can use ifelse inside other functions to quickly create new data.

Summary

ifelse lets you pick values based on a condition for many items at once.

It returns a new vector with values chosen from 'yes' or 'no' options.

Use it to quickly label, replace, or change values without loops.