Ruby, how to shuffle one array into another

array_shuffle_into.rb

# Inspired in the answers: http://stackoverflow.com/questions/4908413/how-to-initialize-an-array-in-one-step-using-ruby

class Array
  def shuffle_into(array)
    a1 = self.dup
    a2 = array.dup

    (a1.size + a2.size).times.map do
      [true, false].sample ? (a1.shift || a2.shift) : (a2.shift || a1.shift)
    end
  end
end