The Art of R Programming - Index of

54 CHAPTER 5. LISTS
> lapply(list(1:3,25:27),median)
[[1]]
[1] 2
[[2]]
[1] 26
In this example the list was created only as a temporary measure, so we should convert back to numeric:
> as.numeric(lapply(list(1:3,25:27),median))
[1] 2 26
5.9 Size of a List
You can obtain the number of elements in a list via length():
> length(j)
[1] 3
5.10 Recursive Lists
Lists can be recursive, i.e. you can have lists within lists. For instance:
> b c a a
[[1]]
[[1]]$u
[1] 5
[[1]]$v
[1] 12
[[2]]
[[2]]$w
[1] 13
> length(a)
[1] 2
So, a is now a two-element list, with each element itself being a list.