code: def subset(self, *args):
          
          cols = {}
          for k in self.colnames:
              if k in args:
                  cols[str(k)] = \
                      self.__data_columns[self.colnames.index(k)].values
          return DataFrame(**cols)
docs: Subset only some of the columns of the DataFrame.
  
          :param args: list of column names of the object that should be subsetted
          :type args: tuple
          :return: returns dataframe with only the columns you selected
          :rtype: DataFrame