Array#rotate equivalent in ruby 1.8.7

Question

a = [ \"a\", \"b\", \"c\", \"d\" ]
a.rotate         #=> [\"b\", \"c\", \"d\", \"a\"]

#rotate is a method of Array in R

Answer 1

Nothing like coming way late to the party... ;)

Similar to a.rotate!(n):

a += a.shift(n)

And it works with a = []. However, unlike a.rotate!(n), it doesn't do anything if n is greater than the length of a.

The following preserves the value of a and allow n greater than a.length to work, at the expense of being a little more elaborate:

a.last(a.length - (n % a.length)) + a.first(n % a.length)

This would obviously be best if n % a.length is computed once separately and the whole thing wrapped in a method monkey patched into Array.

class Array
  def rot(n)
    m = n % self.length
    self.last(self.length - m) + self.first(m)
  end
end