lapply()

lapply(X, FUN, ...)

lapply() applies a function to every element of a list or vector and returns the results as a list. It is one of the most fundamental functions in R for iteration, forming the foundation for many other apply functions. Unlike sapply() which attempts to simplify the output, lapply() always returns a list, making it predictable and reliable for downstream operations.

Syntax

lapply(X, FUN, ...)

Parameters

Parameter	Type	Default	Description
X	list or vector	—	An atomic object or list to iterate over
FUN	function	—	The function to apply to each element
...	any	—	Additional arguments passed to FUN

Examples

Basic usage with a list

x <- list(a = 1:3, b = 4:6, c = 7:9)
result <- lapply(x, sum)
print(result)
# $a
# [1] 6
# $b
# [1] 15
# $c
# [1] 24

Using additional arguments

x <- list(1, 2, 3, 4, 5)
result <- lapply(x, function(elem, mult) elem * mult, mult = 10)
print(result)
# [[1]]
# [1] 10
# [[2]]
# [1] 20
# [[3]]
# [1] 30
# [[4]]
# [1] 40
# [[5]]
# [1] 50

Working with data frame columns

df <- data.frame(
  a = c(1, 2, 3),
  b = c(4, 5, 6),
  c = c(7, 8, 9)
)
result <- lapply(df, mean)
print(result)
# $a
# [1] 2
# $b
# [1] 5
# $c
# [1] 8

Common Patterns

Combining with unlist for vector output: When you need a vector instead of a list, chain unlist() or use sapply() directly.

x <- list(1, 2, 3)
# Get numeric vector instead of list
vec <- unlist(lapply(x, function(i) i^2))
print(vec)
# [1] 1 4 9

Using lapply with anonymous functions: Define functions inline for quick operations without naming them.

strings <- list("hello", "world", "r")
upper <- lapply(strings, toupper)
print(upper)
# [[1]]
# [1] "HELLO"
# [[2]]
# [1] "WORLD"
# [[3]]
# [1] "R"

See Also

• base::sapply
• base::apply
• purrr::map