code: def _to_integral(self, output_array):
          
          if self.dtype == int64_dtype:
              group_labels = output_array
              null_label = self.missing_value
          elif self.dtype == categorical_dtype:
              # Coerce LabelArray into an isomorphic array of ints.  This is
              # necessary because np.where doesn't know about LabelArrays or the
              # void dtype.
              group_labels = output_array.as_int_array()
              null_label = output_array.missing_value_code
          else:
              raise AssertionError(
                  "Unexpected Classifier dtype: %s." % self.dtype
              )
          return group_labels, null_label
docs: Convert an array produced by this classifier into an array of integer
          labels and a missing value label.