code: def adding_temp_index(self, ddf):
      # Adds a temporary index to allow for merging features and targets later
      ddf["dummy"] = 1
      ddf[INDEX_TMP_COL] = ddf["dummy"].cumsum()
      del ddf["dummy"]
      return ddf
  
imports: import gc
  import logging
  import os
  import shutil
  from functools import reduce
  from typing import Optional
  import nvtabular
  from merlin.core.dispatch import HAS_GPU
  from merlin.schema import Tags
  from nvtabular import ops
  from .args_parsing import parse_arguments
label_desc: Use image node_id 6 for calling the PreprocessingRunner obj's underlying member method code with example usage: obj.adding_temp_index(ddf) and returns: ddf