Safer deep transform_hash from http://avdi.org/devblog/2009/11/20/hash-transforms-in-ruby/

gistfile1.rb

    def transform_hash(original, options={}, &block)  
      options[:safe_descent] ||= {}
      new_hash = {}
      options[:safe_descent][original.object_id] = new_hash
      original.inject(new_hash) { |result, (key,value)|  
        if (options[:deep] && Hash === value)
          value = options[:safe_descent].fetch( value.object_id ) {
                    transform_hash(value, options, &block)
                  }
        end
        block.call(result,key,value)  
        result  
      }  
    end