org.apache.mahout.cf.taste.hadoop.item.ItemIDIndexReducer 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.hadoop.item;

import java.io.IOException;

import org.apache.hadoop.mapreduce.Reducer;
import org.apache.mahout.math.VarIntWritable;
import org.apache.mahout.math.VarLongWritable;

public final class ItemIDIndexReducer extends
    Reducer {

  private final VarLongWritable minimumItemIDWritable = new VarLongWritable();

  @Override
  protected void reduce(VarIntWritable index,
                        Iterable possibleItemIDs,
                        Context context) throws IOException, InterruptedException {
    long minimumItemID = Long.MAX_VALUE;
    for (VarLongWritable varLongWritable : possibleItemIDs) {
      long itemID = varLongWritable.get();
      if (itemID < minimumItemID) {
        minimumItemID = itemID;
      }
    }
    if (minimumItemID != Long.MAX_VALUE) {
      minimumItemIDWritable.set(minimumItemID);
      context.write(index, minimumItemIDWritable);
    }
  }
  
}