/*
* 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.snapshot;
import it.unimi.dsi.fastutil.longs.Long2IntMap;
import it.unimi.dsi.fastutil.longs.Long2IntOpenHashMap;
import it.unimi.dsi.fastutil.longs.Long2ObjectMap;
import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
import org.grouplens.lenskit.core.Transient;
import org.grouplens.lenskit.cursors.Cursor;
import org.grouplens.lenskit.data.dao.EventDAO;
import org.grouplens.lenskit.data.dao.SortOrder;
import org.grouplens.lenskit.data.event.Rating;
import org.grouplens.lenskit.data.pref.Preference;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.inject.Inject;
import javax.inject.Provider;
import java.util.Random;
/**
* A Factory that creates PackedRatingBuildSnapshots from an opened
* DataAccessObject.
*/
public class PackedPreferenceSnapshotBuilder implements Provider<PackedPreferenceSnapshot> {
private static final Logger logger = LoggerFactory.getLogger(PackedPreferenceSnapshotBuilder.class);
private final EventDAO dao;
private Random random;
@Inject
public PackedPreferenceSnapshotBuilder(@Transient EventDAO dao, Random random) {
this.dao = dao;
this.random = random;
}
@Override
public PackedPreferenceSnapshot get() {
logger.debug("Packing preference snapshot");
PackedPreferenceDataBuilder bld = new PackedPreferenceDataBuilder();
// Track the indices where everything appears for finding previous
// rating info for a user-item pair
Long2ObjectMap<Long2IntMap> uiIndexes =
new Long2ObjectOpenHashMap<Long2IntMap>(2000);
// Since we iterate in timestamp order, we can just overwrite
// old data for a user-item pair with new data.
Cursor<Rating> ratings = dao.streamEvents(Rating.class, SortOrder.TIMESTAMP);
try {
for (Rating r : ratings) {
final long user = r.getUserId();
final long item = r.getItemId();
final Preference p = r.getPreference();
// get the item -> index map for this user
Long2IntMap imap = uiIndexes.get(user);
if (imap == null) {
imap = new Long2IntOpenHashMap();
imap.defaultReturnValue(-1);
uiIndexes.put(user, imap);
}
// have we seen the item?
final int index = imap.get(item);
if (index < 0) { // we've never seen (user,item) before
// if this is not an unrate (a no-op), add the pref
if (p != null) {
int idx = bld.add(p);
imap.put(item, idx);
}
} else { // we have seen this rating before
if (p == null) {
// free the entry, no rating here
bld.release(index);
imap.put(item, -1);
} else {
// just overwrite the previous value
bld.set(index, p);
}
}
}
logger.debug("Packed {} ratings", bld.size());
} finally {
ratings.close();
}
bld.shuffle(random);
PackedPreferenceData data = bld.build();
return new PackedPreferenceSnapshot(data);
}
}