org.apache.mahout.cf.taste.impl.recommender

Class ItemUserAverageRecommender

java.lang.Object

org.apache.mahout.cf.taste.impl.recommender.AbstractRecommender

org.apache.mahout.cf.taste.impl.recommender.ItemUserAverageRecommender

All Implemented Interfaces:

Refreshable, Recommender

public final class ItemUserAverageRecommender
extends AbstractRecommender

Like ItemAverageRecommender, except that estimated preferences are adjusted for the users' average preference value. For example, say user X has not rated item Y. Item Y's average preference value is 3.5. User X's average preference value is 4.2, and the average over all preference values is 4.0. User X prefers items 0.2 higher on average, so, the estimated preference for user X, item Y is 3.5 + 0.2 = 3.7.

Constructor Summary

Constructors

Constructor and Description
ItemUserAverageRecommender(DataModel dataModel)

Method Summary

Modifier and Type	Method and Description
float	estimatePreference(long userID, long itemID)
List<RecommendedItem>	recommend(long userID, int howMany, IDRescorer rescorer, boolean includeKnownItems)
void	refresh(Collection<Refreshable> alreadyRefreshed) Triggers "refresh" -- whatever that means -- of the implementation.
void	removePreference(long userID, long itemID) Default implementation which just calls DataModel.removePreference(long, long) (Object, Object)}.
void	setPreference(long userID, long itemID, float value) Default implementation which just calls DataModel.setPreference(long, long, float).
String	toString()

Methods inherited from class org.apache.mahout.cf.taste.impl.recommender.AbstractRecommender

getAllOtherItems, getDataModel, getDefaultCandidateItemsStrategy, recommend, recommend, recommend

Methods inherited from class java.lang.Object

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

Constructor Detail

ItemUserAverageRecommender

public ItemUserAverageRecommender(DataModel dataModel)
                           throws TasteException

Throws:

TasteException

Method Detail

recommend

public List<RecommendedItem> recommend(long userID,
                                       int howMany,
                                       IDRescorer rescorer,
                                       boolean includeKnownItems)
                                throws TasteException

Parameters:

userID - user for which recommendations are to be computed

howMany - desired number of recommendations

rescorer - rescoring function to apply before final list of recommendations is determined

includeKnownItems - whether to include items already known by the user in recommendations

Returns:

List of recommended RecommendedItems, ordered from most strongly recommend to least

Throws:

TasteException - if an error occurs while accessing the DataModel

estimatePreference

public float estimatePreference(long userID,
                                long itemID)
                         throws TasteException

Parameters:

userID - user ID whose preference is to be estimated

itemID - item ID to estimate preference for

Returns:

an estimated preference if the user has not expressed a preference for the item, or else the user's actual preference for the item. If a preference cannot be estimated, returns Double.NaN

Throws:

TasteException - if an error occurs while accessing the DataModel

setPreference

public void setPreference(long userID,
                          long itemID,
                          float value)
                   throws TasteException

Description copied from class: AbstractRecommender

Default implementation which just calls DataModel.setPreference(long, long, float).

Specified by:

setPreference in interface Recommender

Overrides:

setPreference in class AbstractRecommender

Parameters:

userID - user to set preference for

itemID - item to set preference for

value - preference value

Throws:

TasteException - if an error occurs while accessing the DataModel

removePreference

public void removePreference(long userID,
                             long itemID)
                      throws TasteException

Description copied from class: AbstractRecommender

Default implementation which just calls DataModel.removePreference(long, long) (Object, Object)}.

Specified by:

removePreference in interface Recommender

Overrides:

removePreference in class AbstractRecommender

Parameters:

userID - user from which to remove preference

itemID - item for which to remove preference

Throws:

TasteException - if an error occurs while accessing the DataModel

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.

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.

toString

public String toString()

Overrides:

toString in class Object