org.lenskit.basic

Class AbstractItemRecommender

java.lang.Object

org.lenskit.basic.AbstractItemRecommender

All Implemented Interfaces:

ItemRecommender

Direct Known Subclasses:

GreedyRerankingItemRecommender, PopularItemRecommender, RankBlendingItemRecommender, TopNItemRecommender

public abstract class AbstractItemRecommender
extends java.lang.Object
implements ItemRecommender

Base class to ease implementation of item recommenders.

Constructor Summary

Constructors

Constructor and Description
AbstractItemRecommender()

Method Summary

Modifier and Type	Method and Description
java.util.List<java.lang.Long>	recommend(long user) Recommend all possible items for a user using the default exclude set.
java.util.List<java.lang.Long>	recommend(long user, int n) Recommend up to n items for a user using the default exclude set.
protected java.util.List<java.lang.Long>	recommend(long user, int n, LongSet candidates, LongSet exclude) Primary method for implementing an item recommender without details.
java.util.List<java.lang.Long>	recommend(long user, int n, java.util.Set<java.lang.Long> candidates, java.util.Set<java.lang.Long> exclude) Produce a set of recommendations for the user.
protected abstract ResultList	recommendWithDetails(long user, int n, LongSet candidates, LongSet exclude) Primary method for implementing an item recommender.
ResultList	recommendWithDetails(long user, int n, java.util.Set<java.lang.Long> candidates, java.util.Set<java.lang.Long> exclude) Produce a set of recommendations for the user with additional details.

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractItemRecommender

public AbstractItemRecommender()

Method Detail

recommend

public java.util.List<java.lang.Long> recommend(long user)

Recommend all possible items for a user using the default exclude set.

This implementation delegates to recommend(long, int) with a length of -1.

Specified by:

recommend in interface ItemRecommender

Parameters:

user - The user ID.

Returns:

The recommended items.

See Also:

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

recommend

public java.util.List<java.lang.Long> recommend(long user,
                                                int n)

Recommend up to n items for a user using the default exclude set.

This implementation delegates to recommend(long, int, Set, Set) with a length of -1 and null sets.

Specified by:

recommend in interface ItemRecommender

Parameters:

user - The user ID.

n - The number of recommendations to return. Negative values request as many recommendations as possible.

Returns:

The recommended items.

See Also:

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

recommend

public java.util.List<java.lang.Long> recommend(long user,
                                                int n,
                                                @Nullable
                                                java.util.Set<java.lang.Long> candidates,
                                                @Nullable
                                                java.util.Set<java.lang.Long> exclude)

Produce a set of recommendations for the user. This is the most general recommendation method, allowing the recommendations to be constrained by both a candidate set \(\mathcal{C}\) and an exclude set \(\mathcal{E}\). The exclude set is applied to the candidate set, so the final effective candidate set is \(\mathcal{C} \backslash \mathcal{E}\).

The recommender is not guaranteed to return a full n recommendations. There are many reasons why it might return a shorter list, including lack of items, lack of coverage for items, or a predefined notion of a maximum recommendation list length. However, a negative value for n instructs the recommender to return as many as it can consistent with any limitations built in to its design and/or supporting algorithms.

This implementation delegates to recommend(long, int, LongSet, LongSet).

Specified by:

recommend in interface ItemRecommender

Parameters:

user - The user’s ID

n - The number of ratings to return. If negative, the recommender will return as many recommendations as possible.

candidates - A set of candidate items which can be recommended. If null, all items are considered candidates.

exclude - A set of items to be excluded. If null, a default exclude set is used.

Returns:

A list of recommended items.

recommend

protected java.util.List<java.lang.Long> recommend(long user,
                                                   int n,
                                                   @Nullable
                                                   LongSet candidates,
                                                   @Nullable
                                                   LongSet exclude)

Primary method for implementing an item recommender without details. The default implementation delegates to recommendWithDetails(long, int, LongSet, LongSet).

Parameters:

user - The user ID.

n - The number of recommendations to produce, or a negative value to produce unlimited recommendations.

candidates - The candidate items, or null for default.

exclude - The exclude set, or null for default.

Returns:

The result list.

See Also:

recommend(long, int, Set, Set)

recommendWithDetails

public ResultList recommendWithDetails(long user,
                                       int n,
                                       @Nullable
                                       java.util.Set<java.lang.Long> candidates,
                                       @Nullable
                                       java.util.Set<java.lang.Long> exclude)

Description copied from interface: ItemRecommender

Produce a set of recommendations for the user with additional details. This method functions identically to ItemRecommender.recommend(long, int, Set, Set), except that it may produce more detailed results. Implementations may return subclasses of ResultList that provide access to additional details about each recommendation.

Specified by:

recommendWithDetails in interface ItemRecommender

Parameters:

user - The user’s ID

n - The number of ratings to return. If negative, then the recommender will return as many recommendations as possible.

candidates - A set of candidate items which can be recommended. If null, all items are considered candidates.

exclude - A set of items to be excluded. If null, a default exclude set is used.

Returns:

A list of recommended items. If the recommender cannot assign meaningful scores, the scores will be Double.NaN. For most scoring recommenders, the items will be ordered in decreasing order of score. This is not a hard requirement — e.g. set recommenders are allowed to be more flexible.

recommendWithDetails

protected abstract ResultList recommendWithDetails(long user,
                                                   int n,
                                                   @Nullable
                                                   LongSet candidates,
                                                   @Nullable
                                                   LongSet exclude)

Primary method for implementing an item recommender.

Parameters:

user - The user ID.

n - The number of recommendations to produce, or a negative value to produce unlimited recommendations.

candidates - The candidate items, or null for default.

exclude - The exclude set, or null for default.

Returns:

The result list.

See Also:

recommendWithDetails(long, int, Set, Set)