org.apache.mahout.cf.taste.impl.similarity

Class SpearmanCorrelationSimilarity

java.lang.Object

org.apache.mahout.cf.taste.impl.similarity.SpearmanCorrelationSimilarity

All Implemented Interfaces:

Refreshable, UserSimilarity

public final class SpearmanCorrelationSimilarity
extends Object
implements UserSimilarity

Like PearsonCorrelationSimilarity, but compares relative ranking of preference values instead of preference values themselves. That is, each user's preferences are sorted and then assign a rank as their preference value, with 1 being assigned to the least preferred item.

Constructor Summary

Constructors

Constructor and Description
SpearmanCorrelationSimilarity(DataModel dataModel)

Method Summary

Modifier and Type	Method and Description
void	refresh(Collection<Refreshable> alreadyRefreshed) Triggers "refresh" -- whatever that means -- of the implementation.
void	setPreferenceInferrer(PreferenceInferrer inferrer) Attaches a PreferenceInferrer to the UserSimilarity implementation.
double	userSimilarity(long userID1, long userID2) Returns the degree of similarity, of two users, based on the their preferences.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SpearmanCorrelationSimilarity

public SpearmanCorrelationSimilarity(DataModel dataModel)

Method Detail

userSimilarity

public double userSimilarity(long userID1,
                             long userID2)
                      throws TasteException

Description copied from interface: UserSimilarity

Returns the degree of similarity, of two users, based on the their preferences.

Specified by:

userSimilarity in interface UserSimilarity

Parameters:

userID1 - first user ID

userID2 - second user ID

Returns:

similarity between the users, in [-1,1] or Double.NaN similarity is unknown

Throws:

NoSuchUserException - if either user is known to be non-existent in the data

TasteException - if an error occurs while accessing the data

setPreferenceInferrer

public void setPreferenceInferrer(PreferenceInferrer inferrer)

Description copied from interface: UserSimilarity

Attaches a PreferenceInferrer to the UserSimilarity implementation.

Specified by:

setPreferenceInferrer in interface UserSimilarity

Parameters:

inferrer - PreferenceInferrer

refresh

public void refresh(Collection<Refreshable> alreadyRefreshed)

Description copied from interface: Refreshable

Triggers "refresh" -- whatever that means -- of the implementation. The general contract is that any Refreshable should always leave itself in a consistent, operational state, and that the refresh atomically updates internal state from old to new.

Specified by:

refresh in interface Refreshable

Parameters:

alreadyRefreshed - Refreshables that are known to have already been refreshed as a result of an initial call to a {#refresh(Collection)} method on some object. This ensure that objects in a refresh dependency graph aren't refreshed twice needlessly.