code: def _shorten_all_series(mlforecast_df: pd.DataFrame, max_length: int):
      logger.debug(f"Shortening all series to at most {max_length}")
      return mlforecast_df.groupby(
          MLF_ITEMID, as_index=False, sort=False
      ).tail(max_length)
  
imports: import logging
  import math
  import os
  import time
  from typing import Any, Dict, List, Optional, Tuple
  import numpy
  import pandas
  from sklearn.base import BaseEstimator
  import autogluon.core
  from autogluon.common.utils.log_utils import set_logger_verbosity
  from autogluon.tabular import TabularPredictor
  from autogluon.timeseries.dataset.ts_dataframe import ITEMID, TIMESTAMP, TimeSeriesDataFrame
  from autogluon.timeseries.models.abstract import AbstractTimeSeriesModel
  from autogluon.timeseries.models.local import SeasonalNaiveModel
  from autogluon.timeseries.utils.datetime import get_lags_for_frequency, get_seasonality, get_time_features_for_frequency
  from autogluon.timeseries.utils.forecast import get_forecast_horizon_index_ts_dataframe
  from autogluon.timeseries.utils.warning_filters import warning_filter
label_desc: Use image node_id 6 for calling the AbstractMLForecastModel obj's underlying member method code with example usage: obj._shorten_all_series(mlforecast_df, max_length) and returns: mlforecast_df