java 写一个 map reduce 矩阵相乘的案例

1、写一个工具类用来生成 map reduce 实验 所需 input 文件

下面两个是原始文件

matrix1.txt

1 2 -2 0
3 3 4 -3
-2 0 2 3
5 3 -1 2
-4 2 0 2

matrix2.txt

0 3 -1 2 -3
1 3 5 -2 -1
0 1 4 -1 2
-2 2 -1 1 2

package com.ghc.hadoop;

import java.io.*;

public class Utils {
    public static void main(String[] args){
        generateMatrixFromFile("inputs/matrix1.txt","outputs/outmatrix1.txt");
    }
    public static void generateMatrixFromFile(String src,String target){
        BufferedReader bufferedReader = null;
        BufferedWriter bufferedWriter = null;
        String outStr = null;
        try {
            bufferedReader =  new BufferedReader(new FileReader(src));
            bufferedWriter = new BufferedWriter(new FileWriter(target));
            String line = null;
            Integer row = 1;
            while((line=bufferedReader.readLine())!=null){
                String[] columns = line.split(" ");
                StringBuilder sb = new StringBuilder();
                sb.append(row+"\t");
                for(int i=0;i<columns.length;i++){
                     sb.append((i+1)+"_"+columns[i])
                             .append(",");
                }
                outStr = sb.toString();
                if(sb.toString().endsWith(",")){
                    outStr = sb.substring(0,sb.length()-1);
                }
                bufferedWriter.write(outStr);
                bufferedWriter.newLine();
                bufferedWriter.flush();
                row+=1;
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            if(bufferedReader!=null){
                try{bufferedReader.close();}
                catch (IOException ioe){
                    ioe.printStackTrace();
                }
            }
            if(bufferedWriter!=null){
                try{bufferedWriter.close();}
                catch (IOException ioe){
                    ioe.printStackTrace();
                }
            }
        }
    }
}

利用上面的工具类生成 outmatrix1.txt , outmatrix2.txt 两个文本文件

下面是利用工具类产生的两个文件，会用作 后面 map reduce 的 输入文件

outmatrix1.txt

1	1_1,2_2,3_-2,4_0
2	1_3,2_3,3_4,4_-3
3	1_-2,2_0,3_2,4_3
4	1_5,2_3,3_-1,4_2
5	1_-4,2_2,3_0,4_2

outmatrix2.txt

1	1_0,2_3,3_-1,4_2,5_-3
2	1_1,2_3,3_5,4_-2,5_-1
3	1_0,2_1,3_4,4_-1,5_2
4	1_-2,2_2,3_-1,4_1,5_2

这里稍微介绍下 ， 矩阵相乘的原理， 左矩阵的列与右矩阵的行相乘，如上面的两个

左矩阵 shape : 5x4 , 右矩阵 shape: 4x5 ===> out-> shape : 5x5 这里如果有不理解的地方请找到大学的线性代数老师

下面将要对 右矩阵也就是 outmatrix2.txt 里的矩阵 转置 也就是 行列转换下, 因为可能会有多个 map reduce 作业，所以注意下命名 Mapper1 , Reducer1 等等

package com.ghc.hadoop.mapper;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

import java.io.IOException;

public class Mapper1 extends Mapper<LongWritable,Text,Text,Text> {
    private Text outKey = new Text();
    private Text outValue = new Text();
    /**
     * key: 1
      value: 1 1_0,2_3,3_-1,4_2,5_-3
     本类用于转置矩阵
    */
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String[] rowAndLine = value.toString().split("\t");
        // row 为行号
        String row = rowAndLine[0];
        String lines = rowAndLine[1];
        String[] columns = lines.split(",");
        // ["1_0","2_3","3_-1","4_2","5_-3"]
        for(int i=0;i<columns.length;i++){
            String[] columnAndValue = columns[i].split("_");
            String column = columnAndValue[0];
            String valueStr = columnAndValue[1];
            // column 列号 ， value： 行号_值
            outKey.set(column);
            outValue.set(row+"_"+valueStr);
            context.write(outKey,outValue);
        }
    }
}

reduce 操作

package com.ghc.hadoop.reducer;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;

public class Reducer1 extends Reducer<Text,Text,Text,Text>{
    private Text outKey = new Text();
    private Text outValue = new Text();

    @Override
    protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
        StringBuilder sb = new StringBuilder();
        // column 列号 ， value： 行号_值
        for(Text text:values){
            sb.append(text+",");
        }
        String line = sb.toString();
        if(sb.toString().endsWith(",")){
            line = sb.toString().substring(0,sb.length());
        }

        outKey.set(key);
        outValue.set(line);
        context.write(outKey,outValue);
    }
}

推荐算法

待续。。。