class Hash # Slice a hash to include only the given keys. This is useful for # limiting an options hash to valid keys before passing to a method: # # def search(criteria = {}) # criteria.assert_valid_keys(:mass, :velocity, :time) # end # # search(options.slice(:mass, :velocity, :time)) # # If you have an array of keys you want to limit to, you should splat them: # # valid_keys = [:mass, :velocity, :time] # search(options.slice(*valid_keys)) def slice(*keys) keys.map! { |key| convert_key(key) } if respond_to?(:convert_key, true) keys.each_with_object(self.class.new) { |k, hash| hash[k] = self[k] if has_key?(k) } end # Replaces the hash with only the given keys. # Returns a hash containing the removed key/value pairs. # # { a: 1, b: 2, c: 3, d: 4 }.slice!(:a, :b) # # => {:c=>3, :d=>4} def slice!(*keys) keys.map! { |key| convert_key(key) } if respond_to?(:convert_key, true) omit = slice(*self.keys - keys) hash = slice(*keys) replace(hash) omit end # Removes and returns the key/value pairs matching the given keys. # # { a: 1, b: 2, c: 3, d: 4 }.extract!(:a, :b) # => {:a=>1, :b=>2} # { a: 1, b: 2 }.extract!(:a, :x) # => {:a=>1} def extract!(*keys) keys.each_with_object(self.class.new) { |key, result| result[key] = delete(key) if has_key?(key) } end end