mapreduce 实现pagerank

输入格式：
     A　　1　　B,C,D
　　　B　　1　　C,D
map:
　　  B　　A　　1/3
　  　C　　A　　1/3
　  　D　　A　　1/3
　  　A　　|B,C,D
　  　C　　B　　1/2
　  　D　　B　　1/2
　  　B　　|C,D
reduce:
　　　B　　(1-0.85)+0.85*1/3　　C,D

　　　C　　(1-0.85)+0.85*5/6　　

     D　　(1-0.85)+0.85*5/6
     A    (1-0.85)+0.85*0　　B,C,D

import java.io.IOException;

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

public class PageRankIter {
  private static final double damping = 0.85;

  public static class PRIterMapper extends
      Mapper<LongWritable, Text, Text, Text> {
    public void map(LongWritable key, Text value, Context context)
        throws IOException, InterruptedException {
      String line = value.toString();
      String[] tuple = line.split("\t");
      String pageKey = tuple[0];
      double pr = Double.parseDouble(tuple[1]);

      if (tuple.length > 2) {
        String[] linkPages = tuple[2].split(",");
        for (String linkPage : linkPages) {
          String prValue =
              pageKey + "\t" + String.valueOf(pr / linkPages.length);
          context.write(new Text(linkPage), new Text(prValue));
        }
        context.write(new Text(pageKey), new Text("|" + tuple[2]));
      }
    }
  }

  public static class PRIterReducer extends Reducer<Text, Text, Text, Text> {
    public void reduce(Text key, Iterable<Text> values, Context context)
        throws IOException, InterruptedException {
      String links = "";
      double pagerank = 0;
      for (Text value : values) {
        String tmp = value.toString();

        if (tmp.startsWith("|")) {
          links = "\t" + tmp.substring(tmp.indexOf("|") + 1);// index从0开始
          continue;
        }

        String[] tuple = tmp.split("\t");
        if (tuple.length > 1)
          pagerank += Double.parseDouble(tuple[1]);
      }
      pagerank = (double) (1 - damping) + damping * pagerank; // PageRank的计算迭代公式
      context.write(new Text(key), new Text(String.valueOf(pagerank) + links));
    }

  }

  public static void main(String[] args) throws Exception {
    Configuration conf = new Configuration();
    Job job2 = new Job(conf, "PageRankIter");
    job2.setJarByClass(PageRankIter.class);
    job2.setOutputKeyClass(Text.class);
    job2.setOutputValueClass(Text.class);
    job2.setMapperClass(PRIterMapper.class);
    job2.setReducerClass(PRIterReducer.class);
    FileInputFormat.addInputPath(job2, new Path(args[0]));
    FileOutputFormat.setOutputPath(job2, new Path(args[1]));
    job2.waitForCompletion(true);
  }
}

输入为上述的输出
输入格式为：
    A　　pr
    B　　pr
    ...

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class PageRankViewer {
  public static class PageRankViewerMapper extends
      Mapper<LongWritable, Text, FloatWritable, Text> {
    private Text outPage = new Text();
    private FloatWritable outPr = new FloatWritable();

    public void map(LongWritable key, Text value, Context context)
        throws IOException, InterruptedException {
      String[] line = value.toString().split("\t");
      String page = line[0];
      float pr = Float.parseFloat(line[1]);
      outPage.set(page);
      outPr.set(pr);
      context.write(outPr, outPage);
    }
  }

  /**重载key的比较函数，使其经过shuffle和sort后反序（从大到小）输出**/
  public static class DescFloatComparator extends FloatWritable.Comparator {
    // @Override
    public float compare(WritableComparator a,
        WritableComparable<FloatWritable> b) {
      return -super.compare(a, b);
    }

    public int compare(byte[] b1, int s1, int l1, byte[] b2, int s2, int l2) {
      return -super.compare(b1, s1, l1, b2, s2, l2);
    }
  }

  public static void main(String[] args) throws Exception {
      Configuration conf = new Configuration();
      Job job3 = new Job(conf, "PageRankViewer");
      job3.setJarByClass(PageRankViewer.class);
      job3.setOutputKeyClass(FloatWritable.class);
      job3.setSortComparatorClass(DescFloatComparator.class);
      job3.setOutputValueClass(Text.class);
      job3.setMapperClass(PageRankViewerMapper.class);
      FileInputFormat.addInputPath(job3, new Path(args[0]));
      FileOutputFormat.setOutputPath(job3, new Path(args[1]));
      job3.waitForCompletion(true);
  }
}