docs: def as_dfile(self):
          """
          Return the dataset representation in BMDS .(d) file.
  
          Example
          -------
          >>> print(dataset.as_dfile())
          Dose Incidence NEGATIVE_RESPONSE
          0.000000 5 70
          1.960000 1 48
          5.690000 3 47
          29.750000 14 35
          """
          rows = ["Dose Incidence NEGATIVE_RESPONSE"]
          for i, v in enumerate(self.doses):
              if i >= self.num_dose_groups:
                  continue
              rows.append("%f %d %d" % (self.doses[i], self.incidences[i], self.remainings[i]))
          return "\n".join(rows)