RubyてかRailsか ary.group_by(&:itself).map{|k, v| [k, v.size]}.to_h でいける irb(main):010:0> ary = %w(a b b a c) => ["a", "b", "b", "a", "c"] irb(main):011:0> ary.group_by(&:itself) => {"a"=>["a", "a"], "b"=>["b", "b"], "c"=>["c"]} irb(ma…