/*
* 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.knn.item;
import org.grouplens.lenskit.core.Shareable;
import org.grouplens.lenskit.scored.ScoredId;
import org.grouplens.lenskit.scored.ScoredIdBuilder;
import org.grouplens.lenskit.scored.ScoredIds;
import org.grouplens.lenskit.symbols.Symbol;
import org.grouplens.lenskit.vectors.SparseVector;
import java.io.Serializable;
import static java.lang.Math.abs;
/**
* Neighborhood scorer that computes the weighted average of neighbor scores.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
@Shareable
public class WeightedAverageNeighborhoodScorer implements NeighborhoodScorer, Serializable {
private static final long serialVersionUID = 1L;
public static final Symbol NEIGHBORHOOD_WEIGHT_SYMBOL =
Symbol.of("org.grouplens.lenskit.knn.item.neighborhoodWeight");
@Override
public ScoredId score(long item, Iterable<ScoredId> neighbors, SparseVector scores) {
double sum = 0;
double weight = 0;
int n = 0;
for (ScoredId id: neighbors) {
long oi = id.getId();
double sim = id.getScore();
weight += abs(sim);
sum += sim * scores.get(oi);
n += 1;
}
if (weight > 0) {
ScoredIdBuilder builder = ScoredIds.newBuilder();
return builder.setId(item)
.setScore(sum/weight)
.addChannel(NEIGHBORHOOD_WEIGHT_SYMBOL,weight)
.build();
} else {
return null;
}
}
@Override
public String toString() {
return "[NeighborhoodScorer: WeightedAverage]";
}
}