The Art of R Programming

Applying Functions to Lists

Two functions are handy for applying functions to lists: lapply and sapply.

Using the lapply() and sapply() Functions

The function lapply() (for list apply) works like the matrix apply() function, calling the specified function on each component of a list (or vector coerced to a list) and returning another list. Here’s an example:

> lapply(list(1:3,25:29),median)
[[1]]
[1] 2

[[2]]
[1] 27

R applied median() to 1:3 and to 25:29, returning a list consisting of 2 and 27.

In some cases, such as the example here, the list returned by lapply() could be simplified to a vector or matrix. This is exactly what sapply() (for simplified [l]apply) does.

> sapply(list(1:3,25:29),median)
[1]  2 27

You saw an example of matrix output in ...