org.grouplens.lenskit.basic

Class TopNItemRecommender

java.lang.Object

org.grouplens.lenskit.basic.AbstractItemRecommender

org.grouplens.lenskit.basic.TopNItemRecommender

All Implemented Interfaces:

ItemRecommender

public class TopNItemRecommender
extends AbstractItemRecommender

Recommender that recommends the top N items by a scorer. Implements all methods required by AbstractItemRecommender. The default exclude set is all items rated by the user.

Recommendations are returned in descending order of score.

Since:

1.1

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TopNItemRecommender.Provider An intelligent provider for Top-N recommenders.

Field Summary

Fields

Modifier and Type	Field and Description
protected ItemDAO	itemDAO
protected ItemScorer	scorer
protected UserEventDAO	userEventDAO

Constructor Summary

Constructors

Constructor and Description
TopNItemRecommender(UserEventDAO uedao, ItemDAO idao, ItemScorer scorer)

Method Summary

Modifier and Type	Method and Description
protected LongSet	getDefaultExcludes(long user) Get the default exclude set for a user.
protected LongSet	getDefaultExcludes(UserHistory<? extends Event> user) Get the default exclude set for a user.
protected LongSet	getPredictableItems(long user) Determine the items for which predictions can be made for a certain user.
ItemScorer	getScorer()
protected List<ScoredId>	recommend(int n, SparseVector scores) Pick the top n items from a score vector.
protected List<ScoredId>	recommend(long user, int n, LongSet candidates, LongSet exclude) Implement the ID-based recommendation in terms of the scorer.

Methods inherited from class org.grouplens.lenskit.basic.AbstractItemRecommender

recommend, recommend, recommend, recommend

Methods inherited from class java.lang.Object

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

Field Detail

userEventDAO

protected final UserEventDAO userEventDAO

itemDAO

protected final ItemDAO itemDAO

scorer

protected final ItemScorer scorer

Constructor Detail

TopNItemRecommender

@Inject
public TopNItemRecommender(UserEventDAO uedao,
                                   ItemDAO idao,
                                   ItemScorer scorer)

Method Detail

getScorer

public ItemScorer getScorer()

recommend

protected List<ScoredId> recommend(long user,
                                   int n,
                                   LongSet candidates,
                                   LongSet exclude)

Implement the ID-based recommendation in terms of the scorer. This method uses getDefaultExcludes(long) to supply a missing exclude set.

Specified by:

recommend in class AbstractItemRecommender

Parameters:

user - The user ID.

n - The number of items to return, or negative to return all possible items.

candidates - The candidate set, or null to use a default set of candidates.

exclude - The set of excluded items, or null to use the default exclude set.

Returns:

A scored list of item IDs.

See Also:

ItemRecommender.recommend(long, int, Set, Set)

recommend

protected List<ScoredId> recommend(int n,
                                   SparseVector scores)

Pick the top n items from a score vector.

Parameters:

n - The number of items to recommend.

scores - The scored item vector.

Returns:

The top n items from scores, in descending order of score.

getDefaultExcludes

protected LongSet getDefaultExcludes(long user)

Get the default exclude set for a user. The base implementation gets all the items they have interacted with.

Parameters:

user - The user ID.

Returns:

The set of items to exclude.

getDefaultExcludes

protected LongSet getDefaultExcludes(@Nullable
                                     UserHistory<? extends Event> user)

Get the default exclude set for a user. The base implementation returns all the items they have interacted with (from UserHistory.itemSet()).

Parameters:

user - The user history.

Returns:

The set of items to exclude.

getPredictableItems

protected LongSet getPredictableItems(long user)

Determine the items for which predictions can be made for a certain user. This implementation is naive and asks the DAO for all items; subclasses should override it with something more efficient if practical.

Parameters:

user - The user's ID.

Returns:

All items for which predictions can be generated for the user.