MapReduce实现矩阵相乘

时间:2023-07-18 08:33:14

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:



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:

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);
} } }