// Copyright (C) 2011 Zeno Gantner, Chris Newell
//
// This file is part of MyMediaLite.
//
// MyMediaLite is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// MyMediaLite is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with MyMediaLite. If not, see <http://www.gnu.org/licenses/>.
package org.mymedialite.grouprec;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import org.mymedialite.IRecommender;
import org.mymedialite.data.WeightedItem;
/**
* Group recommender that averages user scores.
* @version 2.03
*/
public class Average extends GroupRecommender {
/**
*
*/
public Average(IRecommender recommender) {
super(recommender);
}
/**
*
*/
public List<Integer> rankItems(Collection<Integer> users, Collection<Integer> items) {
List<WeightedItem> average_scores = new ArrayList<WeightedItem>(items.size());
for (int i : items) {
WeightedItem weightedItem = new WeightedItem(i, 0.0);
for (int u : users) {
// TODO consider taking CanPredict into account
weightedItem.weight += recommender.predict(u, i);
}
weightedItem.weight = weightedItem.weight / users.size();
average_scores.add(i, weightedItem);
}
Collections.sort(average_scores, Collections.reverseOrder());
List<Integer> ranked_items = new ArrayList<Integer>(average_scores.size());
for (int i=0; i<average_scores.size(); i++) {
ranked_items.add(i, average_scores.get(i).item_id);
}
return ranked_items;
}
}