/**
* 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.Cache;
import org.apache.mahout.cf.taste.impl.common.FullRunningAverage;
import org.apache.mahout.cf.taste.impl.common.Retriever;
import org.apache.mahout.cf.taste.impl.common.RunningAverage;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.PreferenceArray;
import org.apache.mahout.cf.taste.similarity.PreferenceInferrer;
/**
* <p>
* Implementations of this interface compute an inferred preference for a user and an item that the user has
* not expressed any preference for. This might be an average of other preferences scores from that user, for
* example. This technique is sometimes called "default voting".
* </p>
*/
public final class AveragingPreferenceInferrer implements PreferenceInferrer {
private static final Float ZERO = 0.0f;
private final DataModel dataModel;
private final Cache<Long,Float> averagePreferenceValue;
public AveragingPreferenceInferrer(DataModel dataModel) throws TasteException {
this.dataModel = dataModel;
Retriever<Long,Float> retriever = new PrefRetriever();
averagePreferenceValue = new Cache<Long,Float>(retriever, dataModel.getNumUsers());
refresh(null);
}
@Override
public float inferPreference(long userID, long itemID) throws TasteException {
return averagePreferenceValue.get(userID);
}
@Override
public void refresh(Collection<Refreshable> alreadyRefreshed) {
averagePreferenceValue.clear();
}
private final class PrefRetriever implements Retriever<Long,Float> {
@Override
public Float get(Long key) throws TasteException {
RunningAverage average = new FullRunningAverage();
PreferenceArray prefs = dataModel.getPreferencesFromUser(key);
int size = prefs.length();
if (size == 0) {
return ZERO;
}
for (int i = 0; i < size; i++) {
average.addDatum(prefs.getValue(i));
}
return (float) average.getAverage();
}
}
@Override
public String toString() {
return "AveragingPreferenceInferrer";
}
}