/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.mahout.cf.taste.example.kddcup.track2;
import java.io.File;
import java.io.IOException;
import java.util.Collection;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.example.kddcup.KDDCupDataModel;
import org.apache.mahout.cf.taste.impl.common.FastByIDMap;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.common.LongPrimitiveIterator;
import org.apache.mahout.cf.taste.similarity.ItemSimilarity;
import org.apache.mahout.common.iterator.FileLineIterable;
final class TrackItemSimilarity implements ItemSimilarity {
private final FastByIDMap<TrackData> trackData;
TrackItemSimilarity(File dataFileDirectory) throws IOException {
trackData = new FastByIDMap<TrackData>();
for (String line : new FileLineIterable(KDDCupDataModel.getTrackFile(dataFileDirectory))) {
TrackData trackDatum = new TrackData(line);
trackData.put(trackDatum.getTrackID(), trackDatum);
}
}
@Override
public double itemSimilarity(long itemID1, long itemID2) {
if (itemID1 == itemID2) {
return 1.0;
}
TrackData data1 = trackData.get(itemID1);
TrackData data2 = trackData.get(itemID2);
if (data1 == null || data2 == null) {
return 0.0;
}
// Arbitrarily decide that same album means "very similar"
if (data1.getAlbumID() != TrackData.NO_VALUE_ID && data1.getAlbumID() == data2.getAlbumID()) {
return 0.9;
}
// ... and same artist means "fairly similar"
if (data1.getArtistID() != TrackData.NO_VALUE_ID && data1.getArtistID() == data2.getArtistID()) {
return 0.7;
}
// Tanimoto coefficient similarity based on genre, but maximum value of 0.25
FastIDSet genres1 = data1.getGenreIDs();
FastIDSet genres2 = data2.getGenreIDs();
if (genres1 == null || genres2 == null) {
return 0.0;
}
int intersectionSize = genres1.intersectionSize(genres2);
if (intersectionSize == 0) {
return 0.0;
}
int unionSize = genres1.size() + genres2.size() - intersectionSize;
return intersectionSize / (4.0 * unionSize);
}
@Override
public double[] itemSimilarities(long itemID1, long[] itemID2s) {
int length = itemID2s.length;
double[] result = new double[length];
for (int i = 0; i < length; i++) {
result[i] = itemSimilarity(itemID1, itemID2s[i]);
}
return result;
}
@Override
public long[] allSimilarItemIDs(long itemID) {
FastIDSet allSimilarItemIDs = new FastIDSet();
LongPrimitiveIterator allItemIDs = trackData.keySetIterator();
while (allItemIDs.hasNext()) {
long possiblySimilarItemID = allItemIDs.nextLong();
if (!Double.isNaN(itemSimilarity(itemID, possiblySimilarItemID))) {
allSimilarItemIDs.add(possiblySimilarItemID);
}
}
return allSimilarItemIDs.toArray();
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
// do nothing
}
}