Circular shift of vector by distance n [duplicate]

Question

Say I have

a <- c(1, 2, 3)

and I want b to be derived from a by shifting it in direction "left" by distance 1

b
# [1] 2 3 1

By derivation I mean you either:

1. Pass "a" into a function that spits out "b"
2. You use some sort of indexing short had which does that.
3. b <- c(2, 3, 1), for example, is not a solution I'm looking for

What would be elegant/efficient ways to do that?

Answer 1

You can make use of head and tail to create a function like this:

shifter <- function(x, n = 1) {
  if (n == 0) x else c(tail(x, -n), head(x, n))
}

Usage:

a <- 1:4

shifter(a)
# [1] 2 3 4 1

shifter(a, 2)
# [1] 3 4 1 2

(Or, library(SOfun); shifter(a) where you can get SOfun from here).