code: def build_mock_groupby(self, **kwargs):
      groupby_op = self.inputs[0].op
      return groupby_op.build_mock_groupby(**kwargs)[self.selection]
  
file_path: mars/mars/dataframe/groupby/getitem.py
imports: from collections.abc import Iterable
  from ...None import opcodes
  from ...core import OutputType
  from ...serialization.serializables import AnyField
  from ..operands import DataFrameOperandMixin, DataFrameOperand
  from ..utils import parse_index
label_desc: Use image node_id 4 for calling the GroupByIndex obj's underlying member method code with example usage: obj.build_mock_groupby() and returns: groupby_op