hash.each_pair { |key,value| hash[key] = value.to_a }

来自Hash#to_a的文档

Converts hsh to a nested array of [
key,value ] arrays.

h = { "c" => 300,"a" => 100,"d" => 400,"c" => 300 }

h.to_a #=> [["c",300],["a",100],["d",400]]