/**
 * 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.similarity.item;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.mahout.math.RandomAccessSparseVector;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;
import org.apache.mahout.math.hadoop.DistributedRowMatrix;

import java.io.IOException;

public class ToItemVectorsReducer
    extends Reducer<IntWritable, DistributedRowMatrix.MatrixEntryWritable,IntWritable, VectorWritable> {
  
  @Override
  protected void reduce(IntWritable rowIndex, Iterable<DistributedRowMatrix.MatrixEntryWritable> values, Context ctx)
      throws IOException, InterruptedException {

    Vector vector = new RandomAccessSparseVector(Integer.MAX_VALUE, 100);
    for (DistributedRowMatrix.MatrixEntryWritable entry : values) {
      vector.setQuick(entry.getCol(), entry.getVal());
    }
    VectorWritable vectorWritable = new VectorWritable(vector);
    vectorWritable.setWritesLaxPrecision(true);
    ctx.write(rowIndex, vectorWritable);
  }
}
