docs: def group_cache_valid(self, col_list):
          """
          Checks whether the column has a factorization that exists and is not older than the source
  
          :param col:
          :return:
          """
          cache_valid = False
  
          if self.rootdir:
              col_values_file_check = os.path.join(self.rootdir, self.create_group_base_name(col_list)) + \
                                      '.values/__attrs__'
  
              exists_group_index = os.path.exists(col_values_file_check)
              missing_col_check = [1 for col in col_list if not os.path.exists(self[col].rootdir + '/__attrs__')]
              cache_valid = (exists_group_index and not missing_col_check)
  
          return cache_valid