Feature (machine learning)

A feature is an input attribute or computed representation used by a machine learning system. An example can be represented by a vector whose coordinates are individual feature values; a design matrix commonly places examples in rows and these coordinates in columns. A feature can be measured directly or derived from other measurements.^[ref]

For example, classifying manufactured parts might use measured length and width as two feature inputs. Their ratio is another possible feature, exposing a shape relationship to a simple model. Choosing a representation changes which rules are easy to learn. A variable available only after the desired prediction time can introduce data leakage, while a distributed representation can learn useful coordinates without assigning each one a human-readable meaning.