/*
* 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.baseline;
import javax.inject.Inject;
import javax.inject.Provider;
import org.grouplens.grapht.annotation.DefaultProvider;
import org.grouplens.lenskit.core.Shareable;
import org.grouplens.lenskit.core.Transient;
import org.grouplens.lenskit.cursors.Cursor;
import org.grouplens.lenskit.data.dao.EventDAO;
import org.grouplens.lenskit.data.event.Rating;
import org.grouplens.lenskit.data.pref.Preference;
/**
* Rating scorer that predicts the global mean rating for all items.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
@DefaultProvider(GlobalMeanRatingItemScorer.Builder.class)
@Shareable
public class GlobalMeanRatingItemScorer extends ConstantItemScorer {
/**
* A default builder used to create GlobalMeanPredictors.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public static class Builder implements Provider<GlobalMeanRatingItemScorer> {
private EventDAO dao;
/**
* Construct a new provider.
*
* @param dao The DAO.
*/
@Inject
public Builder(@Transient EventDAO dao) {
this.dao = dao;
}
@Override
public GlobalMeanRatingItemScorer get() {
double avg = computeMeanRating(dao);
return new GlobalMeanRatingItemScorer(avg);
}
}
private static final long serialVersionUID = 1L;
/**
* Construct a new global mean scorer where it is assumed
* that the given value is the global mean.
*
* @param mean The global mean.
*/
public GlobalMeanRatingItemScorer(double mean) {
super(mean);
}
/**
* Utility method to compute the mean or average of the rating values
* contained in the given collection of ratings.
*
* @param dao The DAO to average.
* @return The average of the rating values stored in {@var ratings}.
*/
public static double computeMeanRating(EventDAO dao) {
double total = 0;
long count = 0;
Cursor<Rating> ratings = dao.streamEvents(Rating.class);
try {
for (Rating r : ratings) {
Preference p = r.getPreference();
if (p != null) {
total += p.getValue();
count += 1;
}
}
} finally {
ratings.close();
}
double avg = 0;
if (count > 0) {
avg = total / count;
}
return avg;
}
}