code: def _get_row_sparse(self, arr_list, ctx, row_id):
          
          # get row sparse params based on row ids
          if not isinstance(row_id, ndarray.NDArray):
              raise TypeError("row_id must have NDArray type, but %s is given"%(type(row_id)))
          if not self._trainer:
              raise RuntimeError("Cannot get row_sparse data for Parameter '%s' when no " \
                                 "Trainer is created with it."%self.name)
          results = self._check_and_get(arr_list, ctx)
  
          # fetch row sparse params from the trainer
          self._trainer._row_sparse_pull(self, results, row_id)
          return results
docs: Get row_sparse data from row_sparse parameters based on row_id.