E- the type of object whose features are extracted
public interface FeatureExtractor<E>
FeatureExtractorprovides a method of converting generic input objects into feature vectors. Features themselves are represented as strings. Feature vectors are typically very sparse, so they are represented as maps from objects to numerical values. Numerical values may be any numerical type, such as
For linear classifiers, it is often convenient to include a distinguished feature with a value of 1.0 as part of every vector. This will allow linear classifiers to learn offsets.
ObjectToDoubleMap is useful for incrementally
constructing feature maps.