org.apache.mahout.cf.taste.impl.recommender.AllSimilarItemsCandidateItemsStrategy Maven / Gradle / Ivy

/**
 * 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 com.google.common.base.Preconditions;
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.similarity.ItemSimilarity;

/**
 * returns the result of {@link ItemSimilarity#allSimilarItemIDs(long)} as candidate items
 */
public class AllSimilarItemsCandidateItemsStrategy extends AbstractCandidateItemsStrategy {

  private final ItemSimilarity similarity;

  public AllSimilarItemsCandidateItemsStrategy(ItemSimilarity similarity) {
    Preconditions.checkArgument(similarity != null, "similarity is null");
    this.similarity = similarity;
  }

  @Override
  protected FastIDSet doGetCandidateItems(long[] preferredItemIDs, DataModel dataModel, boolean includeKnownItems)
    throws TasteException {
    FastIDSet candidateItemIDs = new FastIDSet();
    for (long itemID : preferredItemIDs) {
      candidateItemIDs.addAll(similarity.allSimilarItemIDs(itemID));
    }
    if (!includeKnownItems) {
      candidateItemIDs.removeAll(preferredItemIDs);
    }
    return candidateItemIDs;
  }
}