def aggregate(self, stream, group_by=None, operators=None):
        if self._execution_plan:
            self._execution_plan.append('aggregate', 'transform')

        if group_by and operators:
            return stream.groupby(group_by).agg(operators)
        else:
            return None
Return list of compute nodes in all cells, optionally
dataset/ETHPy150Open Convertro/Hydro/src/hydro/transformers.py/Transformers.aggregate--crossover with--dataset/ETHPy150Open BU-NU-CLOUD-SP16/Trusted-Platform-Module-nova/nova/cells/rpcapi.py/CellsAPI.compute_node_get_all