R shortcut to getting last n entries in a vector [duplicate]

Question

This may be redundant but I could not find a similar question on SO.

Is there a shortcut to getting the last n elements/entries in a vector or array without using the length of the vector in the calculation?

foo <- 1:23

> foo
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Let say one wants the last 7 entities, I want to avoid this cumbersome syntax:

> foo[(length(foo)-6):length(foo)]
[1] 17 18 19 20 21 22 23

Python has foo[-7:]. Is there something similar in R? Thanks!

Answer 1

You want the tail function

foo <- 1:23
tail(foo, 5)
#[1] 19 20 21 22 23
tail(foo, 7)
#[1] 17 18 19 20 21 22 23
x <- 1:3
# If you ask for more than is currently in the vector it just
# returns the vector itself.
tail(x, 5)
#[1] 1 2 3

Along with head there are easy ways to grab everything except the last/first n elements of a vector as well.

x <- 1:10
# Grab everything except the first element
tail(x, -1)
#[1]  2  3  4  5  6  7  8  9 10
# Grab everything except the last element
head(x, -1)
#[1] 1 2 3 4 5 6 7 8 9

Answer 2

Not a good idea when you have the awesome tail function but here's an alternative:

n <- 3
rev(rev(foo)[1:n])

I'm preparing myself for the down votes.