/**
* 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.recommender;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.PreferenceArray;
public final class PreferredItemsNeighborhoodCandidateItemsStrategy extends AbstractCandidateItemsStrategy {
/**
* returns all items that have not been rated by the user and that were preferred by another user
* that has preferred at least one item that the current user has preferred too
*/
@Override
protected FastIDSet doGetCandidateItems(long[] preferredItemIDs, DataModel dataModel, boolean includeKnownItems)
throws TasteException {
FastIDSet possibleItemsIDs = new FastIDSet();
for (long itemID : preferredItemIDs) {
PreferenceArray itemPreferences = dataModel.getPreferencesForItem(itemID);
int numUsersPreferringItem = itemPreferences.length();
for (int index = 0; index < numUsersPreferringItem; index++) {
possibleItemsIDs.addAll(dataModel.getItemIDsFromUser(itemPreferences.getUserID(index)));
}
}
if (!includeKnownItems) {
possibleItemsIDs.removeAll(preferredItemIDs);
}
return possibleItemsIDs;
}
}