transform_keys

Returns a new hash with the results of running the block once for every key. This method does not change the values.

h = { a: 1, b: 2, c: 3 }
h.transform_keys {|k| k.to_s }  #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys(&:to_s)        #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys.with_index {|k, i| "#{k}.#{i}" }
                                #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

If no block is given, an enumerator is returned instead.