How to elegantly symbolize_keys for a 'nested' hash

Consider the following code:

  hash1 = {"one" => 1, "two" => 2, "three" => 3}
  hash2 = hash1.reduce({}){ |h, (k,v)| h.merge(k => hash1) }
  hash3 = hash2.reduce({}){ |h, (k,v)| h.merge(k => hash2) }
  hash4 = hash3.reduce({}){ |h, (k,v)| h.merge(k => hash3) }

hash4 is a 'nested' hash i.e. a hash with string keys and similarly 'nested' hash values.

The 'symbolize_keys' method for Hash in Rails lets us easily convert the string keys to symbols. But I'm looking for an elegant way to convert all keys (primary keys plus keys of all hashes within hash4) to symbols.

The point is to save myself from my (imo) ugly solution:

  class Hash
    def symbolize_keys_and_hash_values
      symbolize_keys.reduce({}) do |h, (k,v)|
        new_val = v.is_a?(Hash) ? v.symbolize_keys_and_hash_values : v
        h.merge({k => new_val})
      end
    end
  end
hash4.symbolize_keys_and_hash_values #=> desired result

FYI: Setup is Rails 3.2.17 and Ruby 2.1.1

Update:

Answer is hash4.deep_symbolize_keys for Rails <= 5.0

Answer is JSON.parse(JSON[hash4], symbolize_names: true) for Rails > 5

#ruby-on-rails