/*
* 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.eval.metrics.topn;
import org.grouplens.lenskit.Recommender;
import org.grouplens.lenskit.eval.Attributed;
import org.grouplens.lenskit.eval.data.traintest.TTDataSet;
import org.grouplens.lenskit.eval.metrics.AbstractMetric;
import org.grouplens.lenskit.eval.metrics.ResultColumn;
import org.grouplens.lenskit.eval.traintest.TestUser;
import org.grouplens.lenskit.scored.ScoredId;
import org.grouplens.lenskit.util.statistics.MeanAccumulator;
import java.util.List;
/**
* Metric that measures how long a TopN list actually is.
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public class TopNLengthMetric extends AbstractMetric<MeanAccumulator, TopNLengthMetric.Result, TopNLengthMetric.Result> {
private final String prefix;
private final String suffix;
private final int listSize;
private final ItemSelector candidates;
private final ItemSelector exclude;
public TopNLengthMetric(String pre, String sfx, int listSize, ItemSelector candidates, ItemSelector exclude) {
super(Result.class, Result.class);
prefix = pre;
suffix = sfx;
this.listSize = listSize;
this.candidates = candidates;
this.exclude = exclude;
}
@Override
protected String getPrefix() {
return prefix;
}
@Override
protected String getSuffix() {
return suffix;
}
@Override
public MeanAccumulator createContext(Attributed algo, TTDataSet ds, Recommender rec) {
return new MeanAccumulator();
}
@Override
public Result doMeasureUser(TestUser user, MeanAccumulator context) {
List<ScoredId> recs;
recs = user.getRecommendations(listSize, candidates, exclude);
if (recs == null) {
return null;
}
int n = recs.size();
context.add(n);
return new Result(n);
}
@Override
protected Result getTypedResults(MeanAccumulator context) {
return new Result(context.getMean());
}
public static class Result {
@ResultColumn("TopN.ActualLength")
public final double length;
public Result(double len) {
length = len;
}
}
/**
* Build a Top-N length metric to measure Top-N lists.
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public static class Builder extends TopNMetricBuilder<TopNLengthMetric> {
@Override
public TopNLengthMetric build() {
return new TopNLengthMetric(prefix, suffix, listSize, candidates, exclude);
}
}
}