Reverse a hash in Ruby

Question

How would I reverse the elements in the hash, keeping the same values and keys, but reversing their order in the hash.

Like so:

{ "4" => "happiness", "10" => "cool", "lala" => "54", "1" => "spider" } 

And convert that to:

{ "1" => "spider", "lala" => "54", "10" => "cool", "4" => "happiness" } 

Or, perhaps I could run a each loop backwards, starting from the last element in the hash, rather than the first?

Answer 1

You could convert the Hash to an Array, reverse that, and then convert it back to a Hash:

reversed_h = Hash[h.to_a.reverse] 

Hash#to_a gives you an array of arrays, the inner arrays are simple [key,value] pairs, then you reverse that array using Array#reverse, and Hash[] converts the [key,value] pairs back into a Hash.

Ruby 2.1 adds an Array#to_h method so you can now say:

reversed_h = h.to_a.reverse.to_h 

Answer 2

In Ruby 2.1+ you can combine reverse_each and to_h:

{foo: 1, bar: 2}.reverse_each.to_h #=> {:bar=>2, :foo=>1}