columnize.rb

module Columnizer
  def columnize(k=3)
    result_set = []
    n = self.index(self.last)
    r = (n + 1).to_f / k.to_f
    (0..n).each do |z|
      x = (z.to_f * r).ceil
      x = x - n while x > n
      result_set << self[x]
    end
    result_set
  end

  def columnize!(k=3)
    self.replace columnize(k)
  end
end

class Array
  include Columnizer
end