Ruby 配列で重複した項目のみを取り出す
arr = [1, 2, 3, 2, 4, 1] arr.tally.filter_map { |k, v| k if v > 1 }.sort => [1, 2] arr.group_by{ |i| i }.reject{ |k,v| v.one? }.keys.sort => [1, 2] arr.filter_map{ |i| i if arr.count(i) > 1 }.uniq.sort => [1, 2]
arr = [1, 2, 3, 2, 4, 1] arr.tally.filter_map { |k, v| k if v > 1 }.sort => [1, 2] arr.group_by{ |i| i }.reject{ |k,v| v.one? }.keys.sort => [1, 2] arr.filter_map{ |i| i if arr.count(i) > 1 }.uniq.sort => [1, 2]