code: def _concat(self, egdfs):
          
          egdfs = list(egdfs)
          edata = pd.concat(egdfs, axis=0, ignore_index=False, copy=False)
  
          # groupby can mixup the rows. We try to maintain the original
          # order, but we can only do that if the result has a one to
          # one relationship with the original
          one2one = (
              self.keep_index and
              not any(edata.index.duplicated()) and
              len(edata.index) == len(self.data.index))
          if one2one:
              edata = edata.sort_index()
          else:
              edata.reset_index(drop=True, inplace=True)
  
          # Maybe this should happen in the verb functions
          if self.keep_groups and self.groups:
              edata = GroupedDataFrame(edata, groups=self.groups)
          return edata
docs: Concatenate evaluated group dataframes
  
          Parameters
          ----------
          egdfs : iterable
              Evaluated dataframes
  
          Returns
          -------
          edata : pandas.DataFrame
              Evaluated data