How to use the meshplex.helpers.grp_start_len function in meshplex

def _compute_edges_cells(self):
        """This creates interior edge->cells relations. While it's not
        necessary for many applications, it sometimes does come in handy.
        """
        if self.edges is None:
            self.create_edges()

        num_edges = len(self.edges["nodes"])

        count = numpy.bincount(self.cells["edges"].reshape(-1), minlength=num_edges)

        # 
        edges_flat = self.cells["edges"].flat
        idx_sort = numpy.argsort(edges_flat)
        idx_start, count = grp_start_len(edges_flat[idx_sort])
        res1 = idx_sort[idx_start[count == 1]][:, numpy.newaxis]
        idx = idx_start[count == 2]
        res2 = numpy.column_stack([idx_sort[idx], idx_sort[idx + 1]])
        self._edges_cells = [
            [],  # no edges with zero adjacent cells
            res1 // 3,
            res2 // 3,
        ]
        # self._edges_local = [
        #     [],  # no edges with zero adjacent cells
        #     res1 % 3,
        #     res2 % 3,
        #     ]

        # For each edge, store the number of adjacent cells plus the index into
        # the respective edge array.