/*
* 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.vectors.similarity;
import it.unimi.dsi.fastutil.longs.LongSet;
import org.grouplens.lenskit.collections.LongUtils;
import org.grouplens.lenskit.core.Shareable;
import org.grouplens.lenskit.vectors.MutableSparseVector;
import org.grouplens.lenskit.vectors.SparseVector;
import javax.inject.Inject;
import java.io.Serializable;
/**
* Distance similarity for vectors.
*
* @author <a href="http://www.grouplens.org">GroupLens Research</a>
*/
@Shareable
public class DistanceVectorSimilarity implements VectorSimilarity, Serializable {
private static final long serialVersionUID = 1L;
/**
* Construct a new distance similarity function.
* It computes similarity as (1-|v1-v2|_2). after normalizing vectors to be unit vectors
* Similarity is in range [-1,1];
*/
@Inject
public DistanceVectorSimilarity() {
}
@Override
public double similarity(SparseVector vec1, SparseVector vec2) {
final double distance;
// One of the vector is empty
if (vec1.norm() == 0 || vec2.norm() == 0){
return Double.NaN;
}
LongSet ts = LongUtils.setUnion(vec1.keySet(),vec2.keySet());
MutableSparseVector v1 = MutableSparseVector.create(ts);
v1.fill(0);
v1.set(vec1);
v1.multiply(1.0 / v1.norm());
v1.addScaled(vec2, -1.0 / vec2.norm());
distance = v1.norm();
return 1-distance;
}
@Override
public boolean isSparse() {
return false;
}
@Override
public boolean isSymmetric() {
return true;
}
}