docstr: Unscale the time series dataset's feature column and target column.
  
  :return: the xshardtsdataset instance.
docstr_tok: ["Unscale","the","time","series","dataset","'s","feature","column","and","target","column",".",":","return",":","the","xshardtsdataset","instance","."]
code: def unscale(self):
      """
      Unscale the time series dataset's feature column and target column.
  
      :return: the xshardtsdataset instance.
      """
  
      def _inverse_transform(
          df, id_col, scaler, feature_col, target_col
      ):
          from sklearn.utils.validation import check_is_fitted
          from bigdl.nano.utils.common import invalidInputError
  
          scaler_for_this_id = scaler[df[id_col].iloc[0]]
          invalidInputError(
              not check_is_fitted(scaler_for_this_id),
              "scaler is not fitted. When calling scale for the first time, "
              "you need to set fit=True.",
          )
  
          df[
              target_col + feature_col
          ] = scaler_for_this_id.inverse_transform(
              df[target_col + feature_col]
          )
          return df
  
      self.shards = self.shards.transform_shard(
          _inverse_transform,
          self.id_col,
          self.scaler_dict,
          self.feature_col,
          self.target_col,
      )
      return self
  
imports: from bigdl.orca.data.shard import SparkXShards
  from bigdl.orca.learn.utils import dataframe_to_xshards_of_pandas_df
  from bigdl.chronos.data.utils.utils import _to_list, _check_type
  from bigdl.chronos.data.utils.roll import roll_timeseries_dataframe
  from bigdl.chronos.data.utils.impute import impute_timeseries_dataframe
  from bigdl.chronos.data.utils.split import split_timeseries_dataframe
  from bigdl.chronos.data.experimental.utils import add_row, transform_to_dict
  from bigdl.chronos.data.utils.scale import unscale_timeseries_numpy
  from bigdl.chronos.data.utils.feature import generate_dt_features
  import pandas
label_desc: Use image node_id 6 for calling the XShardsTSDataset obj's underlying member method code with example usage: obj.unscale() and returns: self, df