class_docstr: A preprocessor for tf.data.Dataset.
  
  A preprocessor transforms the dataset using `tf.data` operations.
docstr: Transform the dataset wth the preprocessor.
  
  # Arguments
      dataset: an instance of `tf.data.Dataset`.
  
  # Returns
      The transformed dataset.
code: def transform(self, dataset):
      """Transform the dataset wth the preprocessor.
  
      # Arguments
          dataset: an instance of `tf.data.Dataset`.
  
      # Returns
          The transformed dataset.
      """
      raise NotImplementedError
  
file_path: autokeras/autokeras/engine/preprocessor.py
imports: from autokeras.engine import serializable
label_desc: Use image node_id 2 for calling the Preprocessor obj's underlying member method code with example usage: obj.transform(dataset) without return types