code: def _evaluate_group_dataframe(self, gdf):
          
          gdf._is_copy = None
          result_index = gdf.index if self.keep_index else []
          data = pd.DataFrame(index=result_index)
          for expr in self.expressions:
              value = expr.evaluate(gdf, self.env)
              if isinstance(value, pd.DataFrame):
                  data = value
                  break
              else:
                  _create_column(data, expr.column, value)
          data = _add_group_columns(data, gdf)
          return data
docs: Evaluate a single group dataframe
  
          Parameters
          ----------
          gdf : pandas.DataFrame
              Input group dataframe
  
          Returns
          -------
          out : pandas.DataFrame
              Result data