//Copyright (C) 2010 Steffen Rendle, Zeno Gantner
//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.itemrec;
/**
* Weighted k-nearest neighbor item-based collaborative filtering using cosine similarity.
*
* This recommender does NOT support incremental updates.
* @version 2.03
*/
public class WeightedItemKNN extends ItemKNN {
/**
*
*/
public double predict(int user_id, int item_id) {
if ((user_id < 0) || (user_id > maxUserID))
return 0;
if ((item_id < 0) || (item_id > maxItemID))
return 0;
if (k == Integer.MAX_VALUE) {
return correlation.sumUp(item_id, feedback.userMatrix().get(user_id));
} else {
double result = 0;
for (int neighbor : nearest_neighbors[item_id])
if (feedback.itemMatrix().get(neighbor, user_id))
result += correlation.get(item_id, neighbor);
return result;
}
}
/**
*/
public String toString() {
return "WeightedItemKNN k=" + (k == Integer.MAX_VALUE ? "inf" : Integer.toString(k));
}
}