/*
* 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.slopeone;
import it.unimi.dsi.fastutil.longs.LongIterator;
import it.unimi.dsi.fastutil.longs.LongSet;
import org.grouplens.lenskit.core.Transient;
import org.grouplens.lenskit.data.dao.ItemDAO;
import org.grouplens.lenskit.knn.item.model.ItemItemBuildContext;
import org.grouplens.lenskit.vectors.SparseVector;
import javax.annotation.Nonnull;
import javax.inject.Inject;
import javax.inject.Provider;
/**
* Pre-computes the deviations and number of mutual rating users for every pair
* of items and stores the results in a {@code DeviationMatrix} and
* {@code CoratingMatrix}. These matrices are later used by a
* {@code SlopeOneItemScorer}.
*/
public class SlopeOneModelBuilder implements Provider<SlopeOneModel> {
private final SlopeOneModelDataAccumulator accumulator;
private final ItemItemBuildContext buildContext;
@Inject
public SlopeOneModelBuilder(@Transient @Nonnull ItemDAO dao,
@Transient ItemItemBuildContext context,
@DeviationDamping double damping) {
buildContext = context;
accumulator = new SlopeOneModelDataAccumulator(damping, dao);
}
/**
* Constructs and returns a {@link SlopeOneModel}.
*/
@Override
public SlopeOneModel get() {
LongSet items = buildContext.getItems();
LongIterator outer = items.iterator();
while (outer.hasNext()) {
final long item1 = outer.nextLong();
final SparseVector vec1 = buildContext.itemVector(item1);
LongIterator inner = items.iterator();
while (inner.hasNext()) {
final long item2 = inner.nextLong();
if (item1 != item2) {
SparseVector vec2 = buildContext.itemVector(item2);
accumulator.putItemPair(item1, vec1, item2, vec2);
}
}
}
return new SlopeOneModel(accumulator.buildMatrix());
}
}