class_docstr: Build Preprocessor with a map function.
  
  # Arguments
      func: a callable function for the dataset to map.
code: def transform(self, dataset):
      return dataset.map(self.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 2 for calling the LambdaPreprocessor obj's underlying member method code with example usage: obj.transform(dataset) and returns: dataset