/*
* LensKit, an open source recommender systems toolkit.
* Copyright 2010-2014 LensKit Contributors. See CONTRIBUTORS.md.
* Work on LensKit has been funded by the National Science Foundation under
* grants IIS 05-34939, 08-08692, 08-12148, and 10-17697.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
package org.grouplens.lenskit.basic;
import it.unimi.dsi.fastutil.longs.LongSortedSet;
import org.grouplens.lenskit.ItemScorer;
import org.grouplens.lenskit.collections.LongUtils;
import org.grouplens.lenskit.vectors.ImmutableSparseVector;
import org.grouplens.lenskit.vectors.MutableSparseVector;
import org.grouplens.lenskit.vectors.SparseVector;
import javax.annotation.Nonnull;
import javax.inject.Inject;
/**
* A simple cached item scorer that remembers the result for the last user id it scored.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public class SimpleCachingItemScorer extends AbstractItemScorer{
private long cachedId = -1;
private ImmutableSparseVector cachedScores = null;
private final ItemScorer scorer;
@Inject
public SimpleCachingItemScorer(ItemScorer sc) {
scorer = sc;
}
/**
* For each input, check with the cached user id. If the requested items
* is a subset of the cached items, use the cache; otherwise score the
* new items and update the cached scores.
*/
@Override
public void score(long user, @Nonnull MutableSparseVector scores){
LongSortedSet reqItems = scores.keyDomain();
if(cachedId == user && cachedScores != null) {
LongSortedSet cachedItems = cachedScores.keyDomain();
if(!cachedItems.containsAll(reqItems)) {
LongSortedSet diffItems = LongUtils.setDifference(reqItems, cachedItems);
SparseVector newCache = scorer.score(user, diffItems);
cachedScores = cachedScores.combineWith(newCache);
}
scores.set(cachedScores);
} else {
scorer.score(user, scores);
cachedScores = scores.immutable();
cachedId = user;
}
}
public long getId() {
return cachedId;
}
public SparseVector getCache() {
return cachedScores;
}
}