lapply works over an array or a single element?

Question

I\'m slightly confused as to whether lapply works on a list or on a vector. See two examples below

1. Here, the mean function is applied over an array of numbers,

Answer 1

lapply will work on whatever is the highest level which defines the structure of the R object.

If I have 4 individual integers, lapply will work on each integer:

x <- 1:4

lapply(x, identity)
#[[1]]
#[1] 1
#
#[[2]]
#[1] 2
#
#[[3]]
#[1] 3
#
#[[4]]
#[1] 4

If however I have a list of length==2 each containing 2 values, lapply will work on each list object.

x <- list(1:2,3:4)
lapply(x, identity)
#[[1]]
#[1] 1 2
#
#[[2]]
#[1] 3 4