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Ruby 配列で重複した項目のみを取り出す

Ruby

Last updated at 2022-01-10Posted at 2022-01-06

arr = [1, 2, 3, 2, 4, 1, 5, 5]

arr.tally.filter_map { |k, v| k if v > 1 }.sort
=> [1, 2, 5]

arr.group_by{ |i| i }.reject{ |k,v| v.one? }.keys.sort
=> [1, 2, 5]

arr.filter_map{ |i| i if arr.count(i) > 1 }.uniq.sort
=> [1, 2, 5]

※2022/01/10追記
@jnchito さんから Enumerable#tally を使う方法をご提案いただきました。
https://qiita.com/akinov/items/3dad33174eb9e0c91f39#comment-075b6b4a1a80b624d417

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