com.yassergonzalez.pagerank.PageRankMatrixMapper.java Source code

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Here is the source code for com.yassergonzalez.pagerank.PageRankMatrixMapper.java

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/*
 * Copyright 2014 Yasser Gonzalez <contact@yassergonzalez.com>.
 *
 * 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 com.yassergonzalez.pagerank;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.ShortWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class PageRankMatrixMapper extends Mapper<LongWritable, Text, ShortArrayWritable, ShortArrayWritable> {

    @Override
    public void map(LongWritable inKey, Text inValue, Context context) throws IOException, InterruptedException {

        // This task gets a line from links-simple-sorted.txt that contains the
        // out links of a page v. It produces results with keys (i, j)
        // corresponding to the indexes of the block M_{i,j} in which each
        // link v -> w should be stored. The value is (v, w, degree(v)).

        Configuration conf = context.getConfiguration();
        short blockSize = Short.parseShort(conf.get("pagerank.block_size"));

        String[] lineParts = inValue.toString().split(":\\s+");
        String[] vOutlinks = lineParts[1].split("\\s+");

        ShortWritable[] blockIndexes = new ShortWritable[2];
        blockIndexes[0] = new ShortWritable();
        blockIndexes[1] = new ShortWritable();

        ShortWritable[] blockEntry = new ShortWritable[3];
        blockEntry[0] = new ShortWritable();
        blockEntry[1] = new ShortWritable();
        blockEntry[2] = new ShortWritable();

        int v, w;
        short i, j;

        v = Integer.parseInt(lineParts[0]);
        j = (short) ((v - 1) / blockSize + 1);

        for (int k = 0; k < vOutlinks.length; k++) {
            w = Integer.parseInt(vOutlinks[k]);
            i = (short) ((w - 1) / blockSize + 1);

            // Indexes of the block M_{i,j}.
            blockIndexes[0].set(i);
            blockIndexes[1].set(j);
            // One entry of the block M_{i,j} corresponding to the v -> w link.
            // The sparse block representation also needs information about
            // the degree of the vector v.
            blockEntry[0].set((short) ((v - 1) % blockSize));
            blockEntry[1].set((short) ((w - 1) % blockSize));
            blockEntry[2].set((short) vOutlinks.length);

            context.write(new ShortArrayWritable(blockIndexes), new ShortArrayWritable(blockEntry));
        }
    }
}