ruby - 快速找出重复哈希值的所有键的方法

Question

我有一个散列如下:

hash = {"Monday" => "a", "Tuesday" => "b", "Wednesday" => "c", "Thursday" => "b", "Friday" => "c"}

我想得到一个新的散列:

{"a" => "Monday", "b" => "Tuesday, Thursday" , "c" => "Wednesday, Friday"}

Hash#invert 只给出第一个值并丢失重复的值。有什么有效的方法可以做到这一点？

Answer 1

hash.inject({}){ |h, (k,v)| (h[v] ||= []) << k; h }
=> {"a"=>["Monday"], "b"=>["Tuesday", "Thursday"], "c"=>["Wednesday", "Friday"]}