code: def prepare(self, dataframe):
          
          mapping = DataFrameMapCreator().get_mapping_from_config(self.__config)
          self.__mapper = DataFrameMapper(mapping)
          train, test = split_dataframe_train_test(dataframe, self.__config.get_option_parameter("split", "train_percentage"))
          return self.__get_correct_return_parameters(train, test)
docs: Takes the already cleaned dataframe, splits it into train and test
          and returns the train and test as numpy arrays.
          If the problem is supervised, the target column will be that last one
          of the returned arrays.