docs: def check_dataframe(self, dataframe):
          """Check the given dataframe for the required columns
          """
          required_columns = (
              'a',
              'b',
              'm',
              'n',
              'r',
          )
          for column in required_columns:
              if column not in dataframe:
                  raise Exception('Required column not in dataframe: {0}'.format(
                      column
                  ))