code: def execute_reduce(cls, ctx, op: "DataFrameGroupByOperand"):
      xdf = cudf if op.gpu else pd
      chunk = op.outputs[0]
      input_idx_to_df = dict(op.iter_mapper_data(ctx))
      row_idxes = sorted(input_idx_to_df.keys())
  
      res = []
      for row_idx in row_idxes:
          row_df = input_idx_to_df.get(row_idx, None)
          if row_df is not None:
              res.append(row_df)
      by = None
      if isinstance(res[0], tuple):
          # By is series
          deliver_by = res[0][-1]
          r = []
          part_len = len(res[0])
          part_len -= 1 if not deliver_by else 2
          for n in range(part_len):
              r.append(xdf.concat([it[n] for it in res], axis=0))
          r = tuple(r)
  
          if deliver_by:
              by = [None] * len(res[0][-2])
              for it in res:
                  for i, v in enumerate(it[1]):
                      if isinstance(v, pd.Series):
                          if by[i] is None:
                              by[i] = v
                          else:
                              by[i] = pd.concat([by[i], v], axis=0)
                      else:
                          by[i] = v
      else:
          r = pd.concat(res, axis=0)
  
      if chunk.index_value is not None:
          if isinstance(r, tuple):
              for s in r:
                  s.index.name = chunk.index_value.name
          else:
              r.index.name = chunk.index_value.name
      if by is None:
          ctx[chunk.key] = r
      elif isinstance(r, tuple):
          ctx[chunk.key] = r + (by,)
      else:
          ctx[chunk.key] = (r, by)
  
imports: import itertools
  from functools import partial
  import numpy
  import pandas
  from ...None import opcodes
  from ...core import ENTITY_TYPE, Entity, OutputType
  from ...core.operand import OperandStage, MapReduceOperand
  from ...lib.groupby_wrapper import wrapped_groupby
  from ...serialization.serializables import BoolField, Int32Field, AnyField
  from ...utils import lazy_import, pd_release_version, no_default
  from ..align import align_dataframe_series, align_series_series
  from ..initializer import Series
  from ..core import SERIES_TYPE, SERIES_CHUNK_TYPE
  from ..utils import build_concatenated_rows_frame, hash_dataframe_on, build_df, build_series, parse_index, is_cudf
  from ..operands import DataFrameOperandMixin, DataFrameShuffleProxy
label_desc: Use image node_id 16 for calling the DataFrameGroupByOperand obj's underlying member method code with example usage: obj.execute_reduce(cls, ctx, op) without return types