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[py2rb] sorted key=itemgetter

Posted at

はじめに

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

sorted (Python)

import operator as op
import string
from itertools import count

psms = list(zip(count(), string.ascii_uppercase + string.ascii_lowercase,
            np.arange(0.01, 0.062, 0.001)))
key = op.itemgetter(0)  # 関数を設定
ipsms = iter(psms)
spsms = sorted(ipsms, key=key)  # 今回はここの話

sortedのオプションkeyに関数を指定することにより、その戻り値によってソートすることができます。

分かりやすい記事はこちら

ただし、今回のソート対象の場合、key = lambda x: x[0]でも行けそうな気もしますし、途中のiter()が無くても動作します。

どうすRuby

まずは、小手調べで絶対値の昇順でソートする例。

l_2d = [[2, 10], [1, -30], [-3, 20]]

p l_2d.sort_by{ |x| x.map{ |y| y.abs }.max }

# [[2, 10], [-3, 20], [1, -30]]

ふむふむ。

l_2d = [[2, 10], [1, -30], [-3, 20]]

key = lambda { |x| x.map{ |y| y.abs }.max }
p l_2d.sort_by{ |x| key.call(x) }

# [[2, 10], [-3, 20], [1, -30]]

これで、lambdaによりソート方法を後から変更することが可能に。

メモ

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