/**
* 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 java.util.Collection;
import org.apache.mahout.cf.taste.common.Refreshable;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.common.RefreshHelper;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.similarity.PreferenceInferrer;
import org.apache.mahout.cf.taste.similarity.UserSimilarity;
/**
* <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 extends AbstractItemSimilarity implements UserSimilarity {
public TanimotoCoefficientSimilarity(DataModel dataModel) {
super(dataModel);
}
/**
* @throws UnsupportedOperationException
*/
@Override
public void setPreferenceInferrer(PreferenceInferrer inferrer) {
throw new UnsupportedOperationException();
}
@Override
public double userSimilarity(long userID1, long userID2) throws TasteException {
DataModel dataModel = getDataModel();
FastIDSet xPrefs = dataModel.getItemIDsFromUser(userID1);
FastIDSet yPrefs = dataModel.getItemIDsFromUser(userID2);
int xPrefsSize = xPrefs.size();
int yPrefsSize = yPrefs.size();
if (xPrefsSize == 0 && yPrefsSize == 0) {
return Double.NaN;
}
if (xPrefsSize == 0 || yPrefsSize == 0) {
return 0.0;
}
int intersectionSize =
xPrefsSize < yPrefsSize ? yPrefs.intersectionSize(xPrefs) : xPrefs.intersectionSize(yPrefs);
if (intersectionSize == 0) {
return Double.NaN;
}
int unionSize = xPrefsSize + yPrefsSize - intersectionSize;
return (double) intersectionSize / (double) unionSize;
}
@Override
public double itemSimilarity(long itemID1, long itemID2) throws TasteException {
int preferring1 = getDataModel().getNumUsersWithPreferenceFor(itemID1);
return doItemSimilarity(itemID1, itemID2, preferring1);
}
@Override
public double[] itemSimilarities(long itemID1, long[] itemID2s) throws TasteException {
int preferring1 = getDataModel().getNumUsersWithPreferenceFor(itemID1);
int length = itemID2s.length;
double[] result = new double[length];
for (int i = 0; i < length; i++) {
result[i] = doItemSimilarity(itemID1, itemID2s[i], preferring1);
}
return result;
}
private double doItemSimilarity(long itemID1, long itemID2, int preferring1) throws TasteException {
DataModel dataModel = getDataModel();
int preferring1and2 = dataModel.getNumUsersWithPreferenceFor(itemID1, itemID2);
if (preferring1and2 == 0) {
return Double.NaN;
}
int preferring2 = dataModel.getNumUsersWithPreferenceFor(itemID2);
return (double) preferring1and2 / (double) (preferring1 + preferring2 - preferring1and2);
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
alreadyRefreshed = RefreshHelper.buildRefreshed(alreadyRefreshed);
RefreshHelper.maybeRefresh(alreadyRefreshed, getDataModel());
}
@Override
public String toString() {
return "TanimotoCoefficientSimilarity[dataModel:" + getDataModel() + ']';
}
}