lapply and sapply in R Programming

Introduction

Use lapply and sapply to run a function on each item in a list or vector easily. They help you avoid writing loops.

You want to apply the same calculation to every item in a list.

You have a vector and want to transform each element quickly.

You want to get results back as a list or a simpler vector/matrix.

You want cleaner, shorter code instead of writing loops.

You want to process data step-by-step in a functional style.

Syntax

R Programming

lapply(X, FUN, ...)
sapply(X, FUN, ..., simplify = TRUE, USE.NAMES = TRUE)

X is the list or vector you want to process.

FUN is the function you want to apply to each element.

Examples

Multiply each number in the list by 2, result is a list.

R Programming

lapply(list(1, 2, 3), function(x) x * 2)

Calculate square root of each number, result is a vector.

R Programming

sapply(c(1, 2, 3), sqrt)

Sum each vector inside the list, result is a list with sums.

R Programming

lapply(list(a = 1:3, b = 4:6), sum)

Sum each vector inside the list, result is a named vector with sums.

R Programming

sapply(list(a = 1:3, b = 4:6), sum)

Sample Program

This program doubles each number in a list using both lapply and sapply. It shows the difference in output types.

R Programming

numbers <- list(2, 4, 6)
double_list <- lapply(numbers, function(x) x * 2)
double_vector <- sapply(numbers, function(x) x * 2)

print(double_list)
print(double_vector)

Important Notes

lapply always returns a list, even if the result is simple.

sapply tries to simplify the result to a vector or matrix if possible.

If sapply cannot simplify, it returns a list like lapply.

Summary

lapply and sapply help apply functions to each item in a list or vector.

lapply returns a list, sapply returns a simpler structure if possible.

They make your code shorter and easier to read than loops.