Package org.tribuo.hash

Class HashedFeatureMap

java.lang.Object
org.tribuo.FeatureMap
org.tribuo.ImmutableFeatureMap
org.tribuo.hash.HashedFeatureMap
All Implemented Interfaces:
Serializable, Iterable<VariableInfo>
public final class HashedFeatureMap extends ImmutableFeatureMap
A FeatureMap used by the HashingTrainer to provide feature name hashing and guarantee that the Model does not contain feature name information, but still works with unhashed features names.
See Also:

  • Method Details

    • get

      public VariableIDInfo get(String name)
      Description copied from class: ImmutableFeatureMap
      Gets the VariableIDInfo for this name. Returns null if it's unknown.
      Overrides:
      get in class ImmutableFeatureMap
      Parameters:
      name - The name to lookup.
      Returns:
      The VariableInfo, or null.

    • getID

      public int getID(String name)
      Gets the id number for this feature, returns -1 if it's unknown.
      Overrides:
      getID in class ImmutableFeatureMap
      Parameters:
      name - The name of the feature.
      Returns:
      A non-negative integer if the feature is known, -1 otherwise.

    • setSalt

      public void setSalt(String salt)
      The salt is not serialised with the Model. It must be set after deserialisation to the same value from training time.

      If the salt is invalid it will throw IllegalArgumentException.

      Parameters:
      salt - The salt value. Must be the same as the one from training time.

    • generateHashedFeatureMap

      public static HashedFeatureMap generateHashedFeatureMap(FeatureMap map, Hasher hasher)
      Converts a standard FeatureMap by hashing each entry using the supplied hash function Hasher.

      This preserves the index ordering of the original feature names, which is important for making sure test time performance is good.

      It guarantees any collisions will produce an feature id number lower than the previous feature's number, and so can be easily removed.

      Parameters:
      map - The FeatureMap to hash.
      hasher - The hashing function.
      Returns:
      A HashedFeatureMap.