/**
* 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.eval;
import org.apache.mahout.cf.taste.common.NoSuchItemException;
import org.apache.mahout.cf.taste.common.NoSuchUserException;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastByIDMap;
import org.apache.mahout.cf.taste.impl.common.FullRunningAverage;
import org.apache.mahout.cf.taste.impl.common.RunningAverage;
import org.apache.mahout.cf.taste.model.Preference;
import org.apache.mahout.cf.taste.model.PreferenceArray;
import org.apache.mahout.cf.taste.recommender.Recommender;
import java.util.Map;
/**
* <p>A {@link org.apache.mahout.cf.taste.eval.RecommenderEvaluator} which computes the "root mean squared" difference
* between predicted and actual ratings for users. This is the square root of the average of this difference,
* squared.</p>
*/
public final class RMSRecommenderEvaluator extends AbstractDifferenceRecommenderEvaluator {
private RunningAverage average;
@Override
void reset() {
average = new FullRunningAverage();
}
@Override
void processOneEstimate(float estimatedPreference, Preference realPref) {
double diff = realPref.getValue() - estimatedPreference;
average.addDatum(diff * diff);
}
@Override
double computeFinalEvaluation() {
return Math.sqrt(average.getAverage());
}
@Override
public String toString() {
return "RMSRecommenderEvaluator";
}
}