fun <R> withFeatureExtraction(extraction: (T) -> Option<R>): FeatureExtractorBuilder.OptionsStep<T, R>
Overrides FeatureExtractionStep.withFeatureExtraction
Defines the feature extraction as such which is most likely based on the current subject (but does not need to be).
extraction - A function returning either Some with the corresponding feature or None in case the
extraction cannot be carried out.