code: def pluck(self, value, key=None):
          
          if key:
              return dict(map(lambda x: (data_get(x, key), data_get(x, value)), self.items))
          else:
              results = list(map(lambda x: data_get(x, value), self.items))
  
          return self.__class__(results)
docs: Get a list with the values of a given key.
  
          :rtype: Collection