Hadoop编写矩阵相乘代码

下面是一个简单的Hadoop矩阵相乘代码示例，该示例假设两个矩阵A和B都存储在HDFS中。其中，矩阵A的路径为input/matrixA，矩阵B的路径为input/matrixB，结果将输出到output/matrixC中。

import java.io.IOException;
import java.util.StringTokenizer;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class MatrixMultiplication {

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

    private Text outKey = new Text();
    private Text outValue = new Text();

    public void map(Object key, Text value, Context context
                    ) throws IOException, InterruptedException {
      // 解析输入文件中的行
      StringTokenizer itr = new StringTokenizer(value.toString());
      int rowNum = Integer.valueOf(itr.nextToken());
      int colNum = Integer.valueOf(itr.nextToken());
      int val = Integer.valueOf(itr.nextToken());

      // 将输入矩阵A中的值按列拆分，输出键值对
      if (rowNum == 1) {
        for (int i = 1; i <= colNum; i++) {
          outKey.set(rowNum + "," + i);
          outValue.set("A," + colNum + "," + val);
          context.write(outKey, outValue);
        }
      }
      // 将输入矩阵B中的值按行拆分，输出键值对
      else if (colNum == 1) {
        for (int i = 1; i <= rowNum; i++) {
          outKey.set(i + "," + colNum);
          outValue.set("B," + rowNum + "," + val);
          context.write(outKey, outValue);
        }
      }
    }
  }

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

    private IntWritable result = new IntWritable();

    public void reduce(Text key, Iterable<Text> values,
                       Context context
                       ) throws IOException, InterruptedException {
      // 将输入键值对中的矩阵A和矩阵B的值进行计算
      int[] a = new int[10];
      int[] b = new int[10];
      int idx = 0;
      for (Text val : values) {
        String[] tmp = val.toString().split(",");
        if (tmp[0].equals("A")) {
          a[idx] = Integer.valueOf(tmp[2]);
        }
        else {
          b[idx] = Integer.valueOf(tmp[2]);
        }
        idx++;
      }
      int sum = 0;
      for (int i = 0; i < idx; i++) {
        sum += a[i] * b[i];
      }
      result.set(sum);
      context.write(key, result);
    }
  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job = Job.getInstance(conf, "matrix multiplication");
    job.setJarByClass(MatrixMultiplication.class);
    job.setMapperClass(MatrixMapper.class);
    job.setReducerClass(MatrixReducer.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(Text.class);
    FileInputFormat.addInputPath(job, new Path("input"));
    FileOutputFormat.setOutputPath(job, new Path("output"));
    System.exit(job.waitForCompletion(true) ? 0 : 1);
  }
}

在上述代码中，Mapper将矩阵A和矩阵B中的值拆分为键值对，并以（i，j）为输出键，其中i和j分别表示输出值在结果矩阵C中的行和列。Reducer将输入键值对中的矩阵A和矩阵B的值进行计算，并输出结果。