code: def _iter_groups(self, data):
          
          groups = data.groupby(self.segmentation_col)
  
          for name in self.models:
              yield name, groups.get_group(name)
docs: Iterate over the groups in `data` after grouping by
          `segmentation_col`. Skips any groups for which there
          is no model stored.
  
          Yields tuples of (name, df) where name is the group key
          and df is the group DataFrame.
  
          Parameters
          ----------
          data : pandas.DataFrame
              Must have a column with the same name as `segmentation_col`.