docstr: Data preprocessing before computing the drift scores.
  
  Parameters
  ----------
  x
      Batch of instances.
  
  Returns
  -------
  Preprocessed reference data and new instances.
docstr_tok: ["Data","preprocessing","before","computing","the","drift","scores",".","Parameters","--","--","--","--","--","x","Batch","of","instances",".","Returns","--","--","--","-","Preprocessed","reference","data","and","new","instances","."]
code: def preprocess(
      self, x: Union[np.ndarray, list]
  ) -> Tuple[np.ndarray, np.ndarray]:
      """
      Data preprocessing before computing the drift scores.
  
      Parameters
      ----------
      x
          Batch of instances.
  
      Returns
      -------
      Preprocessed reference data and new instances.
      """
      if self.preprocess_fn is not None:
          x = self.preprocess_fn(x)
          if (
              not self.preprocess_at_init
              and not self.x_ref_preprocessed
          ):
              x_ref = self.preprocess_fn(self.x_ref)
          else:
              x_ref = self.x_ref
          return x_ref, x  # type: ignore[return-value]
      else:
          return self.x_ref, x
  
imports: import logging
  from abc import abstractmethod
  from typing import Callable, Dict, List, Optional, Tuple, Union, Any
  import numpy
  from alibi_detect.base import BaseDetector, concept_drift_dict, DriftConfigMixin
  from alibi_detect.cd.utils import get_input_shape, update_reference
  from alibi_detect.utils.frameworks import has_pytorch, has_tensorflow
  from alibi_detect.utils.statstest import fdr
  from scipy.stats import binom_test, ks_2samp
  from sklearn.model_selection import StratifiedKFold
label_desc: Use image node_id 2 for calling the BaseContextMMDDrift obj's underlying member method code with example usage: obj.preprocess(x) and returns: x_ref,  x, self,  x