ifelse()

ifelse(test, yes, no)

The ifelse() function is R’s vectorized conditional operator. It tests each element of a vector and returns corresponding values from either the yes or no argument. This makes it essential for data transformation tasks where you need to apply conditional logic across entire vectors.

Syntax

ifelse(test, yes, no)

Parameters

Parameter	Type	Default	Description
test	logical vector	—	Condition to evaluate for each element
yes	vector	—	Values returned where test is TRUE
no	vector	—	Values returned where test is FALSE

Examples

Basic usage

x <- 1:5
ifelse(x > 2, "big", "small")
# [1] "small" "small" "big"   "big"   "big"

With strings

scores <- c(85, 92, 78, 55, 90)
result <- ifelse(scores >= 60, "Pass", "Fail")
result
# [1] "Pass" "Pass" "Fail" "Fail" "Pass"

Preserving NA values

x <- c(1, 2, NA, 4, 5)
ifelse(x > 3, "big", "small")
# [1] "small" "small" NA       "big"   "big"

Common Patterns

Recoding values

colors <- c("red", "blue", "red", "green")
ifelse(colors %in% c("red", "blue"), "primary", "other")
# [1] "primary" "primary" "primary" "other"

Creating flags

temperature <- c(15, 22, 18, 30, 25)
hot_day <- ifelse(temperature > 25, 1, 0)
hot_day
# [1] 0 0 0 1 0

Conditional transformation

prices <- c(10, 50, 100, 200, 25)
discounted <- ifelse(prices > 50, prices * 0.9, prices)
discounted
# [1]  10  45  90 180  25

See Also

• which()
• intersect()
• head()