code: def _transform_target(
      ts_analysis: Dict[str, Dict], df: pd.DataFrame, freq, group: tuple
  ):
      df = deepcopy(
          df
      )  # needed because methods like get_level_values actually have undisclosed side effects  # noqa
      transformer = ts_analysis["stl_transforms"][group]["transformer"]
      if (
          isinstance(df.index, pd.MultiIndex)
          and len(df.index.levels) > 1
      ):
          temp_s = df.droplevel(0)
          temp_s.index = pd.date_range(
              start=temp_s.index[0], freq=freq, periods=len(temp_s)
          )
          return transformer.transform(temp_s.to_period())
      elif isinstance(df.index, pd.MultiIndex):
          temp_s = pd.Series(data=df.values)
          temp_s.index = df.index.levels[
              0
          ]  # warning: do not use get_level_values as it removes inferred freq
          return transformer.transform(temp_s.to_period())
      else:
          return transformer.transform(df.to_period())
  
imports: from typing import Dict
  from copy import deepcopy
  import pandas
label_desc: Use image node_id 1 for calling a global function with example usage: _transform_target(ts_analysis, df, freq, group) and returns: transformer, transformer, transformer