org.grouplens.lenskit.baseline

Class ItemMeanRatingItemScorer

java.lang.Object

org.grouplens.lenskit.basic.AbstractItemScorer

org.grouplens.lenskit.baseline.ItemMeanRatingItemScorer

All Implemented Interfaces:

Serializable, ItemScorer

@DefaultProvider(value=ItemMeanRatingItemScorer.Builder.class)
 @Shareable
public class ItemMeanRatingItemScorer
extends AbstractItemScorer
implements Serializable

Rating scorer that returns the item's mean rating for all predictions. If the item has no ratings, the global mean rating is returned. This implements the baseline scorer p_u,i = µ + b_i, where b_i is the item's average rating (less the global mean µ).

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ItemMeanRatingItemScorer.Builder A builder to create ItemMeanPredictors.

Constructor Summary

Constructors

Constructor and Description
ItemMeanRatingItemScorer(ImmutableSparseVector itemMeans, double globalMean, double damping) Construct a new scorer.

Method Summary

Modifier and Type	Method and Description
void	score(long user, MutableSparseVector items) Score items in a vector.
String	toString()

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

score, score

Methods inherited from class java.lang.Object

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

Constructor Detail

ItemMeanRatingItemScorer

public ItemMeanRatingItemScorer(ImmutableSparseVector itemMeans,
                                double globalMean,
                                double damping)

Construct a new scorer. This assumes ownership of the provided map.

Parameters:

itemMeans - A map of item IDs to their mean ratings.

globalMean - The mean rating value for all items.

damping - The damping factor.

Method Detail

score

public void score(long user,
                  @Nonnull
                  MutableSparseVector items)

Description copied from interface: ItemScorer

Score items in a vector. The key domain of the provided vector is the items to score, and the score method sets the values for each item to its score (or unsets it, if no score can be provided). The previous values are discarded.

Specified by:

score in interface ItemScorer

Parameters:

user - The user ID.

items - The score vector.

toString

public String toString()

Overrides:

toString in class Object