code: def call_agg(self):
      return self._call_agg
  
imports: import numpy
  import pandas
  from ...None import opcodes
  from ...core import OutputType
  from ...core.custom_log import redirect_custom_log
  from ...serialization.serializables import BoolField, TupleField, DictField, AnyField
  from ...utils import enter_current_session, quiet_stdio
  from ..operands import DataFrameOperandMixin, DataFrameOperand
  from ..utils import build_empty_df, build_empty_series, parse_index
label_desc: Use image node_id 5 for calling the GroupByTransform obj's underlying member method code with example usage: obj.call_agg() and returns: self