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はじめに

移植やってます。
( from python 3.7 to ruby 2.7 )

product (Python)

import itertools

A = [('a', 'b', 'c'), ('d', 'e'), ('f', 'g')]

print(list(itertools.product(*A)))

# [('a', 'd', 'f'), ('a', 'd', 'g'), ('a', 'e', 'f'), ('a', 'e', 'g'), ('b', 'd', 'f'), ('b', 'd', 'g'), ('b', 'e', 'f'), ('b', 'e', 'g'), ('c', 'd', 'f'), ('c', 'd', 'g'), ('c', 'e', 'f'), ('c', 'e', 'g')]

ジェネレータ式の入れ子になった for ループとおよそ等価です。たとえば product(A, B) は ((x,y) for x in A for y in B) と同じものを返します。

ふむふむ。

product 失敗 (Ruby)

A = [['a', 'b', 'c'], ['d', 'e'], ['f', 'g']]

print(A.inject(:product))

# [[["a", "d"], "f"], [["a", "d"], "g"], [["a", "e"], "f"], [["a", "e"], "g"], [["b", "d"], "f"], [["b", "d"], "g"], [["b", "e"], "f"], [["b", "e"], "g"], [["c", "d"], "f"], [["c", "d"], "g"], [["c", "e"], "f"], [["c", "e"], "g"]] 

単に、injectすると、平坦化されていない状態で出力されます。

product + flatten 成功 (Ruby)

A = [['a', 'b', 'c'], ['d', 'e'], ['f', 'g']]

print(A.inject(:product).map(&:flatten))

# [["a", "d", "f"], ["a", "d", "g"], ["a", "e", "f"], ["a", "e", "g"], ["b", "d", "f"], ["b", "d", "g"], ["b", "e", "f"], ["b", "e", "g"], ["c", "d", "f"], ["c", "d", "g"], ["c", "e", "f"], ["c", "e", "g"]]

tupleではないのですが、同様の処理ができました。

product 応用問題 (Python)

import itertools

A = [(('H-', 'a'), 'b', 'c'), ('d', 'e'), ('f', 'g')]

print(list(itertools.product(*A)))

# [(('H-', 'a'), 'd', 'f'), (('H-', 'a'), 'd', 'g'), (('H-', 'a'), 'e', 'f'), (('H-', 'a'), 'e', 'g'), ('b', 'd', 'f'), 
('b', 'd', 'g'), ('b', 'e', 'f'), ('b', 'e', 'g'), ('c', 'd', 'f'), ('c', 'd', 'g'), ('c', 'e', 'f'), ('c', 'e', 'g')]

前回は、要素が一つずつでしたが、今回は要素数が異なります。

product 応用問題 (Ruby)

A = [[['H-', 'a'], 'b', 'c'], ['d', 'e'], ['f', 'g']]

print(A.inject(:product).map(&:flatten))

# [["H-", "a", "d", "f"], ["H-", "a", "d", "g"], ["H-", "a", "e", "f"], ["H-", "a", "e", "g"], ["b", "d", "f"], ["b", "d", "g"], ["b", "e", "f"], ["b", "e", "g"], ["c", "d", "f"], ["c", "d", "g"], ["c", "e", "f"], ["c", "e", "g"]]

print(A.inject(:product).map{ _1.flatten(1) }) # 1
print(A[0].product(*A[1..-1]))                 # 2

# [[["H-", "a"], "d", "f"], [["H-", "a"], "d", "g"], [["H-", "a"], "e", "f"], [["H-", "a"], "e", "g"], ["b", "d", "f"], ["b", "d", "g"], ["b", "e", "f"], ["b", "e", "g"], ["c", "d", "f"], ["c", "d", "g"], ["c", "e", "f"], ["c", "e", "g"]]

単なるflattenですと平坦化しすぎですので、深さを指定します。

2番目の書き方は、こちらを参照しました。

メモ

  • Python の itertools.product を学習した
  • 百里を行く者は九十里を半ばとす
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