class_docstr: Build Preprocessor with a map function.
  
  # Arguments
      func: a callable function for the dataset to map.
code: def __init__(self, func, **kwargs):
      super().__init__(**kwargs)
      self.func = func
  
imports: import tensorflow
  from autokeras import analysers
  from autokeras import keras_layers
  from autokeras import preprocessors
  from autokeras.engine import preprocessor
  from autokeras.utils import data_utils
label_desc: Use image node_id 1 to create a new LambdaPreprocessor object from inherited base classes: preprocessor with example: obj = LambdaPreprocessor(func)