matrix ops

 A,0,0,1

A,0,1,2

A,1,0,3

A,1,1,4

B,0,0,5

B,0,1,6

B,1,0,7

B,1,1,8

======================================

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Job;

import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MatrixDriver {

    public static void main(String[] args) throws Exception {

        if (args.length != 2) {

            System.err.println("Usage: MatrixDriver <input> <output>");

            System.exit(-1);

        }

        Configuration conf = new Configuration();

        Job job = new Job(conf, "Matrix Multiplication");

        job.setJarByClass(MatrixDriver.class);

        job.setMapperClass(MatrixMapper.class);

        job.setReducerClass(MatrixReducer.class);

        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(Text.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));

        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        System.exit(job.waitForCompletion(true) ? 0 : 1);

    }

}

===================================================================

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Mapper;

import java.io.IOException;

public class MatrixMapper extends Mapper<Object, Text, Text, Text> {

    public void map(Object key, Text value, Context context)

            throws IOException, InterruptedException {

        // Input format: MatrixName,i,j,value

        // Example: A,0,0,2

        String[] parts = value.toString().split(",");

        String matrix = parts[0];

        int i = Integer.parseInt(parts[1]);

        int j = Integer.parseInt(parts[2]);

        int val = Integer.parseInt(parts[3]);

        int N = 2;  // assume 2x2 matrices for simplicity

        if (matrix.equals("A")) {

            // A[i][k] goes to all C[i][j]

            for (int col = 0; col < N; col++) {

                context.write(new Text(i + "," + col),

                        new Text("A," + j + "," + val));

            }

        } else {

            // B[k][j] goes to all C[i][j]

            for (int row = 0; row < N; row++) {

                context.write(new Text(row + "," + j),

                        new Text("B," + i + "," + val));

            }

        }

    }

}

================================================

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;

public class MatrixReducer extends Reducer<Text, Text, Text, Text> {

    public void reduce(Text key, Iterable<Text> values, Context context)

            throws IOException, InterruptedException {

        // For simplicity, assume max 10 values

        int[] Aval = new int[10];

        int[] Bval = new int[10];

        for (Text t : values) {

            String[] parts = t.toString().split(",");

            String m = parts[0];

            int index = Integer.parseInt(parts[1]);

            int val = Integer.parseInt(parts[2]);

            if (m.equals("A")) {

                Aval[index] = val;

            } else {

                Bval[index] = val;

            }

        }

        int sum = 0;

        for (int k = 0; k < 10; k++) {

            sum += Aval[k] * Bval[k];

        }

        context.write(key, new Text(Integer.toString(sum)));

    }

}