配列同士の中身の掛け算（適当メモ）

kakezan.rb

class Array
  def *(arr)
    self.each_with_index.map{|e,i| e*arr[i] }
  end
end



[3,4,5] * [6,-7,8] #=> [18,-28,40]
[[1,2],[3,4]] * [[-2,-3],[-3,-4]] #=> [[-2, -6], [-9, -16]]