code: def fit(self, x_train, y_train):
      for model in self.models.values():
          model.fit(np.array(x_train), np.array(y_train))
  
imports: from typing import Any, Dict, List, Optional, Union
  import copy
  import numpy
  import pandas
  import xgboost
  import gc
  from collections import defaultdict
  from gluonts.core.component import equals, validated
label_desc: Use image node_id 2 for calling the QuantileReg obj's underlying member method code with example usage: obj.fit(x_train, y_train) without return types