MatrixAdd.java

import java.io.IOException;
import java.util.*;

import org.apache.hadoop.conf.*;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.*;
import org.apache.hadoop.mapreduce.lib.output.*;
import org.apache.hadoop.util.GenericOptionsParser;

public class MatrixAdd 
{

	public static class MatrixAddMapper extends Mapper<Object, Text, Text, IntWritable>
	{
		private final static IntWritable i_value = new IntWritable(1);
		private Text word = new Text();

		public void map(Object key, Text value, Context context) throws IOException, InterruptedException 
		{
			StringTokenizer itr = new StringTokenizer(value.toString());
			int row_id = Integer.parseInt(itr.nextToken().trim());
			int col_id = Integer.parseInt(itr.nextToken().trim());
			int m_value = Integer.parseInt(itr.nextToken().trim());
			word.set(row_id + "," + col_id);
			i_value.set(m_value);
			context.write(word, i_value);
		}
	}

	public static class MatrixAddReducer extends Reducer<Text,IntWritable,Text,IntWritable> 
	{
		private IntWritable result = new IntWritable();

		public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException 
		{
			int sum = 0;
			for (IntWritable val : values) 
			{
				sum += val.get();
			}
			result.set(sum);
			context.write(key, result);
		}
	}

	public static void main(String[] args) throws Exception 
	{
		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
		if (otherArgs.length != 2) 
		{
			System.err.println("Usage: MatrixAdd <in> <out>");
			System.exit(2);
		}
		Job job = new Job(conf, "Matrix Add");
		job.setJarByClass(MatrixAdd.class);
		job.setMapperClass(MatrixAddMapper.class);
		job.setCombinerClass(MatrixAddReducer.class);
		job.setReducerClass(MatrixAddReducer.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
		FileSystem.get(job.getConfiguration()).delete( new Path(otherArgs[1]), true);
		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}