docs: def remove_frequencies(self, fmin, fmax):
          """Remove frequencies from the dataset
          """
          self.data.query(
              'frequency > {0} and frequency < {1}'.format(fmin, fmax),
              inplace=True
          )
          g = self.data.groupby('frequency')
          print('Remaining frequencies:')
          print(sorted(g.groups.keys()))