/**
* 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.impl.similarity;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.similarity.ItemSimilarity;
import org.apache.mahout.cf.taste.similarity.PreferenceInferrer;
import org.apache.mahout.cf.taste.similarity.UserSimilarity;
import org.apache.mahout.cf.taste.impl.common.RefreshHelper;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.Item;
import org.apache.mahout.cf.taste.model.Preference;
import org.apache.mahout.cf.taste.model.User;
import java.util.Collection;
/**
* <p>An implementation of a "similarity" based on the
* <a href="http://en.wikipedia.org/wiki/Jaccard_index#Tanimoto_coefficient_.28extended_Jaccard_coefficient.29">
* Tanimoto coefficient</a>,
* or extended <a href="http://en.wikipedia.org/wiki/Jaccard_index">Jaccard coefficient</a>.</p>
*
* <p>This is intended for "binary" data sets where a user either expresses a generic "yes" preference
* for an item or has no preference. The actual preference values do not matter here, only their presence
* or absence.</p>
*
* <p>The value returned is in [0,1].</p>
*/
public final class TanimotoCoefficientSimilarity implements UserSimilarity, ItemSimilarity {
private final DataModel dataModel;
public TanimotoCoefficientSimilarity(DataModel dataModel) {
this.dataModel = dataModel;
}
/**
* @throws UnsupportedOperationException
*/
@Override
public void setPreferenceInferrer(PreferenceInferrer inferrer) {
throw new UnsupportedOperationException();
}
@Override
public double userSimilarity(User user1, User user2) {
if (user1 == null || user2 == null) {
throw new IllegalArgumentException("user1 or user2 is null");
}
Preference[] xPrefs = user1.getPreferencesAsArray();
Preference[] yPrefs = user2.getPreferencesAsArray();
if (xPrefs.length == 0 && yPrefs.length == 0) {
return Double.NaN;
}
if (xPrefs.length == 0 || yPrefs.length == 0) {
return 0.0;
}
Preference xPref = xPrefs[0];
Preference yPref = yPrefs[0];
Item xIndex = xPref.getItem();
Item yIndex = yPref.getItem();
int xPrefIndex = 1;
int yPrefIndex = 1;
int intersectionSize = 0;
while (true) {
int compare = xIndex.compareTo(yIndex);
if (compare == 0) {
intersectionSize++;
}
if (compare <= 0) {
if (xPrefIndex == xPrefs.length) {
break;
}
xPref = xPrefs[xPrefIndex++];
xIndex = xPref.getItem();
}
if (compare >= 0) {
if (yPrefIndex == yPrefs.length) {
break;
}
yPref = yPrefs[yPrefIndex++];
yIndex = yPref.getItem();
}
}
int unionSize = xPrefs.length + yPrefs.length - intersectionSize;
return (double) intersectionSize / (double) unionSize;
}
@Override
public double itemSimilarity(Item item1, Item item2) throws TasteException {
if (item1 == null || item2 == null) {
throw new IllegalArgumentException("item1 or item2 is null");
}
int preferring1and2 = dataModel.getNumUsersWithPreferenceFor(item1.getID(), item2.getID());
int preferring1 = dataModel.getNumUsersWithPreferenceFor(item1.getID());
int preferring2 = dataModel.getNumUsersWithPreferenceFor(item2.getID());
return (double) preferring1and2 / (double) (preferring1 + preferring2 - preferring1and2);
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
alreadyRefreshed = RefreshHelper.buildRefreshed(alreadyRefreshed);
RefreshHelper.maybeRefresh(alreadyRefreshed, dataModel);
}
@Override
public String toString() {
return "TanimotoCoefficientSimilarity[dataModel:" + dataModel + ']';
}
}