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

Introduction

Here is the source code for nl.tudelft.graphalytics.mapreducev2.conversion.DirectedVertexReducer.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 list of edges in both directions for a single vertex to a single line of output.
 *
 * @author Tim Hegeman
 */
public class DirectedVertexReducer extends Reducer<LongWritable, EdgeData, NullWritable, Text> {

    private Text outValue = new Text();

    @Override
    protected void reduce(LongWritable key, Iterable<EdgeData> values, Context context)
            throws IOException, InterruptedException {
        // Fill separate buffers for incoming and outgoing edges
        StringBuffer sbIn = new StringBuffer();
        StringBuffer sbOut = new StringBuffer();

        // Loop through the messages and add them to the buffers
        boolean foundIn = false, foundOut = false;
        for (EdgeData edge : values) {
            if (edge.getTargetId() == key.get()) {
                // Ignore, this self-edge was added to force this vertex's existence
            } else if (edge.isOutgoing()) {
                if (foundOut)
                    sbOut.append(',');
                sbOut.append(edge.getTargetId());
                foundOut = true;
            } else {
                if (foundIn)
                    sbIn.append(',');
                sbIn.append(edge.getTargetId());
                foundIn = true;
            }
        }

        // Combine the vertex ID and neighbour lists using Marcin's format
        StringBuffer out = new StringBuffer(key.toString());
        out.append("\t#").append(sbIn.toString()).append("\t@").append(sbOut.toString());
        if (!foundOut)
            out.append('\t');

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

}