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

Class CachingItemSimilarity

java.lang.Object

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

All Implemented Interfaces:

Refreshable, ItemSimilarity

public final class CachingItemSimilarity
extends Object
implements ItemSimilarity

Caches the results from an underlying ItemSimilarity implementation.

Constructor Summary

Constructors

Constructor and Description
CachingItemSimilarity(ItemSimilarity similarity, DataModel dataModel) Creates this on top of the given ItemSimilarity.
CachingItemSimilarity(ItemSimilarity similarity, int maxCacheSize) Creates this on top of the given ItemSimilarity.

Method Summary

Modifier and Type	Method and Description
long[]	allSimilarItemIDs(long itemID)
void	clearCacheForItem(long itemID)
double[]	itemSimilarities(long itemID1, long[] itemID2s) A bulk-get version of ItemSimilarity.itemSimilarity(long, long).
double	itemSimilarity(long itemID1, long itemID2) Returns the degree of similarity, of two items, based on the preferences that users have expressed for the items.
void	refresh(Collection<Refreshable> alreadyRefreshed) Triggers "refresh" -- whatever that means -- of the implementation.

Methods inherited from class java.lang.Object

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

Constructor Detail

CachingItemSimilarity

public CachingItemSimilarity(ItemSimilarity similarity,
                             DataModel dataModel)
                      throws TasteException

Creates this on top of the given ItemSimilarity. The cache is sized according to properties of the given DataModel.

Throws:

TasteException

CachingItemSimilarity

public CachingItemSimilarity(ItemSimilarity similarity,
                             int maxCacheSize)

Creates this on top of the given ItemSimilarity. The cache size is capped by the given size.

Method Detail

itemSimilarity

public double itemSimilarity(long itemID1,
                             long itemID2)
                      throws TasteException

Description copied from interface: ItemSimilarity

Returns the degree of similarity, of two items, based on the preferences that users have expressed for the items.

Specified by:

itemSimilarity in interface ItemSimilarity

Parameters:

itemID1 - first item ID

itemID2 - second item ID

Returns:

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

Throws:

NoSuchItemException - if either item is known to be non-existent in the data

TasteException - if an error occurs while accessing the data

itemSimilarities

public double[] itemSimilarities(long itemID1,
                                 long[] itemID2s)
                          throws TasteException

Description copied from interface: ItemSimilarity

A bulk-get version of ItemSimilarity.itemSimilarity(long, long).

Specified by:

itemSimilarities in interface ItemSimilarity

Parameters:

itemID1 - first item ID

itemID2s - second item IDs to compute similarity with

Returns:

similarity between itemID1 and other items

Throws:

NoSuchItemException - if any item is known to be non-existent in the data

TasteException - if an error occurs while accessing the data

allSimilarItemIDs

public long[] allSimilarItemIDs(long itemID)
                         throws TasteException

Specified by:

allSimilarItemIDs in interface ItemSimilarity

Returns:

all IDs of similar items, in no particular order

Throws:

TasteException

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.

clearCacheForItem

public void clearCacheForItem(long itemID)