docs: def _create_related_chart(self, data, work, output_dir):
          """Generates and writes to a file in `output_dir` the data used to
          display a grouped bar chart.
  
          This data gives, for each "maybe" work, the percentage of it
          that is shared with `work`, and the percentage of `work` that
          is shared with the "maybe" work.
  
          :param data: data to derive the chart data from
          :type data: `pandas.DataFrame`
          :param works: work to show related data for
          :type works: `str`
          :param output_dir: directory to output data file to
          :type output_dir: `str`
  
          """
          chart_data = data[work].dropna().sort_values(by=SHARED_RELATED_WORK,
                                                       ascending=False)
          csv_path = os.path.join(output_dir, 'related_{}.csv'.format(work))
          chart_data.to_csv(csv_path)