code: def execute_combine(
      cls, op, in_data: pd.DataFrame
  ) -> Union[pd.DataFrame, pd.Series]:
      return cls._get_execute_combine_result(op, in_data)
  
file_path: mars/mars/dataframe/groupby/nunique.py
imports: from typing import List, Union
  import pandas
  from ...core import OutputType
  from ...utils import implements
  from .aggregation import DataFrameGroupByAgg
  from .custom_aggregation import DataFrameCustomGroupByAggMixin, register_custom_groupby_agg_func
label_desc: Use image node_id 7 for calling the DataFrameCustomGroupByNuniqueMixin obj's underlying member method code with example usage: obj.execute_combine(cls, op, in_data) and returns: cls