nl.tudelft.graphalytics.mapreducev2.conversion.UndirectedVertexReducer.java Source code

Introduction

Here is the source code for nl.tudelft.graphalytics.mapreducev2.conversion.UndirectedVertexReducer.java

Source

/**
 * Copyright 2015 Delft University of Technology
 *
 * Licensed 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 nl.tudelft.graphalytics.mapreducev2.conversion;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

/**
 * Reduces a set of incoming edges for a vertex to a single line of ourput.
 *
 * @author Tim Hegeman
 */
public class UndirectedVertexReducer extends Reducer<LongWritable, LongWritable, NullWritable, Text> {

    private Text outValue = new Text();

    @Override
    protected void reduce(LongWritable key, Iterable<LongWritable> values, Context context)
            throws IOException, InterruptedException {
        // Combine the vertex ID and neighbour IDs using a StringBuilder
        StringBuilder sb = new StringBuilder();
        sb.append(key.get());
        for (LongWritable neighbour : values) {
            sb.append(' ').append(neighbour.get());
        }

        // Output the constructed line
        outValue.set(sb.toString());
        context.write(NullWritable.get(), outValue);
    }

}