array.rb

class Array

  def columnize(n=1)
    rows = []
    y = (self.size / n.to_f).ceil
    nmulti = (0...n).map {|n| y * n}
    y.times do |x|
      rows << self.values_at(*nmulti.map {|z| z + x}).compact
    end
    rows
  end

end