code: def execute(cls, ctx, op: "GroupByIndex"):
      in_data = ctx[op.inputs[0].key]
      ctx[op.outputs[0].key] = in_data[op.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 7 for calling the GroupByIndex obj's underlying member method code with example usage: obj.execute(cls, ctx, op) without return types