docs: def save_summaries(frames, keys, selected_summaries, batch_dir, batch_name):
      """Writes the summaries to csv-files
  
      Args:
          frames: list of ``cellpy`` summary DataFrames
          keys: list of indexes (typically run-names) for the different runs
          selected_summaries: list defining which summary data to save
          batch_dir: directory to save to
          batch_name: the batch name (will be used for making the file-name(s))
  
      Returns: a pandas DataFrame with your selected summaries.
  
      """
      if not frames:
          logger.info("Could save summaries - no summaries to save!")
          logger.info("You have no frames - aborting")
          return None
      if not keys:
          logger.info("Could save summaries - no summaries to save!")
          logger.info("You have no keys - aborting")
          return None
  
      selected_summaries_dict = create_selected_summaries_dict(selected_summaries)
      summary_df = pd.concat(frames, keys=keys, axis=1)
      # saving the selected summaries
      for key, value in selected_summaries_dict.items():
          _summary_file_name = os.path.join(batch_dir, "summary_%s_%s.csv" % (
          key, batch_name))
          _summary_df = summary_df.iloc[:,
                        summary_df.columns.get_level_values(1) == value]
          # include function to tweak headers here (need to learn MultiIndex)
          _header = _summary_df.columns
          _summary_df.to_csv(_summary_file_name, sep=";")
          logger.info(
              "saved summary (%s) to:\n       %s" % (key, _summary_file_name))
      logger.info("finished saving summaries")
      return summary_df