/*
* 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.data.pref;
import it.unimi.dsi.fastutil.longs.Long2DoubleOpenHashMap;
import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.grouplens.lenskit.vectors.MutableSparseVector;
import java.util.Collection;
/**
* Utility class for working with preferences.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
public final class Preferences {
private Preferences() {}
/**
* Construct a new preference builder.
* @return A new preference builder.
*/
public static PreferenceBuilder newBuilder() {
return new PreferenceBuilder();
}
/**
* Create a new preference.
* @param uid The user ID.
* @param iid The item ID.
* @param val The value.
* @return A preference with the specified properties.
*/
public static Preference make(long uid, long iid, double val) {
return new SimplePreference(uid, iid, val);
}
/**
* Compute a user preference vector.
*
* @param prefs The user's preferences.
* @return A vector of the preferences.
* @throws IllegalArgumentException if the same item appears multiple times, or there are
* preferences from multiple users.
*/
public static MutableSparseVector userPreferenceVector(Collection<? extends Preference> prefs) {
// find keys and pre-validate data
Long2DoubleOpenHashMap prefMap = new Long2DoubleOpenHashMap(prefs.size());
long user = 0;
for (Preference p : prefs) {
final long iid = p.getItemId();
if (prefMap.isEmpty()) {
user = p.getUserId();
} else if (user != p.getUserId()) {
throw new IllegalArgumentException("multiple user IDs in pref array");
}
if (prefMap.containsKey(iid)) {
throw new IllegalArgumentException("item " + iid + " occurs multiple times");
} else {
prefMap.put(iid, p.getValue());
}
}
return MutableSparseVector.create(prefMap);
}
/**
* Compute the hash code of a preference. Used to implement {@link #hashCode()} in preference
* implementations.
* @param preference The preference.
* @return The preference's hash code.
*/
public static int hashPreference(Preference preference) {
HashCodeBuilder hcb = new HashCodeBuilder();
return hcb.append(preference.getUserId())
.append(preference.getItemId())
.append(preference.getValue())
.toHashCode();
}
/**
* Compare two preferences for equality. Used to implement {@link #equals(Object)} in preference
* implementations.
* @param p1 The first preference.
* @param p2 The second preference.
* @return Whether the two preferences are equal.
*/
public static boolean equals(Preference p1, Preference p2) {
if (p1 == p2) {
return true;
} else if (p1 == null || p2 == null) {
return false;
}
EqualsBuilder eqb = new EqualsBuilder();
return eqb.append(p1.getUserId(), p2.getUserId())
.append(p1.getItemId(), p2.getItemId())
.append(p1.getValue(), p2.getValue())
.isEquals();
}
}