MapReduce实现矩阵相乘

矩阵相乘能够查看百度百科的解释http://baike.baidu.com/view/2455255.htm?fr=aladdin

有a和b两个矩阵

a:                1   2   3

4   5   0

7   8   9

10  11  12

b:              10  15

0     2

11   9

c = a*b

1:将矩阵存到HDFS中：

矩阵a：

行	列	值	hdfs存储
1	1	1	1,1,1
1	2	2	1,2,2
1	3	3	1,3,3
2	1	4	2,1,4
2	2	5	2,2,5
2	3	0	0不存储
3	1	7	3,1,7
3	2	8	3,2,8
3	3	9	3,3,9
4	1	10	4,1,10
4	2	11	4,2,11
4	3	12	4,3,12

矩阵b：

行	列	值	hdfs存储
1	1	10	1,1,10
1	2	15	1,2,15
2	1	0	0不存储
2	2	2	2,2,2
3	1	11	3,1,11
3	2	9	3,2,9

2:a的map读取

读取第一个值是1,1,1。它是矩阵a的第一行第一列。那么它要在计算c(1,1) c(1,2)的时候使用（这里c仅仅用2列，假设用n列，那么它的值要在计算c(1,1),c(1,2),c(1,3)...c(1,n)的时候使用）。我们就以 key = 1,1  value = a,1,1  ，      key= 1,2   value = a,1,1输出两条数据(1,1) (1,2)是 c(1,1) ,c(1,2)的坐标。

b的map读取

读取第一个值是1,1,10。它是矩阵b的第一行第一列。那么它要在计算c(1,1) c(2,1) c(3,1) c(4,1)的时候使用（这里c仅仅用4行，假设用m行，那么它的值要在计算c(1,1),c(2,1),c(3,1)...c(m,1)的时候使用）。我们就以 key = 1,1  value = b,1,10  ,     key= 2,1   value = b,1,10               ，    key = 3,1   value = b,1,10    ,                                        
key= 4,1   value = b,1,10输出

3:reduce读取计算

通过mapA和mapB的输出能够得到 key = 1,1   ，   value=a,1,1    value=b,1,10   value=a,2,2      value=a,3,3  value = b,3,11l来计算c(1,1)的值

代码例如以下：

package MyMatrix;

import java.io.IOException;
import java.util.Iterator;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.MultipleInputs;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MartrixMultiply{

	/**
	 * 最后得到的矩阵的列数
	 */
	public static final int COL_COUNT = 2;

	/**
	 * 最后得到的矩阵的行数
	 */
	public static final int ROW_COUNT = 4;

	/**
	 * A矩阵的列数或者是B矩阵的行数
	 */
	public static final int BROW_ACOL= 3;

	public static class MartrixMaperA extends Mapper<LongWritable, Text, Text, Text>{

		@Override
		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {

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

			int rowIndex = Integer.parseInt(items[0]);
			int colIndex = Integer.parseInt(items[1]);
			int valueInt = Integer.parseInt(items[2]);

			Text outKey = null;
			Text outValue = null;
			for(int i=0;i<COL_COUNT;i++){
				outKey = new Text(rowIndex + "," + (i+1));
				outValue = new Text("a,"+colIndex+","+valueInt);
				context.write(outKey, outValue);
			}

		}

	}

	public static class MartrixMaperB extends Mapper<LongWritable, Text, Text, Text>{

		@Override
		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {

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

			int rowIndex = Integer.parseInt(items[0]);
			int colIndex = Integer.parseInt(items[1]);
			int valueInt = Integer.parseInt(items[2]);

			Text outKey = null;
			Text outValue = null;
			for(int i=0;i<ROW_COUNT;i++){
				outKey = new Text((i+1) + "," + colIndex);
				outValue = new Text("b,"+rowIndex+","+valueInt);
				context.write(outKey, outValue);
			}

		}

	}

	public static class MartrixReducer extends Reducer<Text,Text,Text,IntWritable>{

		@Override
		protected void reduce(Text key, Iterable<Text> values,Context context)
				throws IOException, InterruptedException {

			String[] items = new String[3];

			int[] valueA = new int[BROW_ACOL];
			int[] valueB = new int[BROW_ACOL];

			Iterator<Text> it = values.iterator();
			while(it.hasNext()){
				items = it.next().toString().split(",");
				if(items[0].equals("a")){
					valueA[Integer.parseInt(items[1])-1] = Integer.parseInt(items[2]);
				}else if(items[0].equals("b")){
					valueB[Integer.parseInt(items[1])-1] = Integer.parseInt(items[2]);
				}
			}

			int result = 0;
			for(int i=0;i<BROW_ACOL;i++){
				result += valueA[i]*valueB[i];
			}
			context.write(key, new IntWritable(result));
		}

	}

	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

		Path pathA = new Path("hdfs://localhost:9000/Martrix/a.txt");
		Path pathB = new Path("hdfs://localhost:9000/Martrix/b.txt");
		Path pathOut = new Path("hdfs://localhost:9000/Martrix/out");

		Configuration conf = new Configuration();
		Job job = new Job(conf,"MartrixMultiply");

		job.setJarByClass(MartrixMultiply.class);

		MultipleInputs.addInputPath(job, pathA, TextInputFormat.class, MartrixMaperA.class);
		MultipleInputs.addInputPath(job, pathB, TextInputFormat.class, MartrixMaperB.class);

		job.setReducerClass(MartrixReducer.class);

		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(Text.class);

		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);

		FileOutputFormat.setOutputPath(job, pathOut);

		if(job.waitForCompletion(true)){
			System.exit(0);
		}else{
			System.exit(1);
		}

	}

}