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MR找共同朋友，数据格式如下：

 

A B C D E FB A C D EC A B ED A B EE A B C DF A

 

第一字母表示本人，其他是他的朋友，找出有共同朋友的人，和共同朋友是谁

 

1 import java.io.IOException; 2 import java.util.Set; 3 import java.util.StringTokenizer; 4 import java.util.TreeSet; 5  6 import org.apache.hadoop.conf.Configuration; 7 import org.apache.hadoop.fs.Path; 8 import org.apache.hadoop.io.Text; 9 import org.apache.hadoop.mapreduce.Job;10 import org.apache.hadoop.mapreduce.Mapper;11 import org.apache.hadoop.mapreduce.Reducer;12 import org.apache.hadoop.mapreduce.Mapper.Context;13 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;14 import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;15 import org.apache.hadoop.util.GenericOptionsParser;16 17 public class FindFriend {18         19           public static class ChangeMapper extends Mapper
     
      {                      20                    @Override21                    public void map(Object key, Text value, Context context) throws IOException, InterruptedException {22                              StringTokenizer itr = new StringTokenizer(value.toString());23                                  Text owner = new Text();24                                  Set
      
        set = new TreeSet
       
        ();25                              owner.set(itr.nextToken());26                              while (itr.hasMoreTokens()) {27                                      set.add(itr.nextToken());28                              }             29                              String[] friends = new String[set.size()];30                              friends = set.toArray(friends);31                              32                              for(int i=0;i
        
          {                          42                         public void reduce(Text key, Iterable
         
           values, 43                                         Context context) throws IOException, InterruptedException {44                                   String  commonfriends =""; 45                               for (Text val : values) {46                                   if(commonfriends == ""){47                                           commonfriends = val.toString();48                                   }else{49                                           commonfriends = commonfriends+":"+val.toString();50                                   }51                                }52                               context.write(key, new Text(commonfriends));                                53                         }                          54           }55           56 57         public static void main(String[] args) throws IOException,58         InterruptedException, ClassNotFoundException {59                 60             Configuration conf = new Configuration();61             String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();62             if (otherArgs.length < 2) {63               System.err.println("args error");64               System.exit(2);65             }66             Job job = new Job(conf, "word count");67             job.setJarByClass(FindFriend.class);68             job.setMapperClass(ChangeMapper.class);69             job.setCombinerClass(FindReducer.class);70             job.setReducerClass(FindReducer.class);71             job.setOutputKeyClass(Text.class);72             job.setOutputValueClass(Text.class);73             for (int i = 0; i < otherArgs.length - 1; ++i) {74               FileInputFormat.addInputPath(job, new Path(otherArgs[i]));75             }76             FileOutputFormat.setOutputPath(job,77               new Path(otherArgs[otherArgs.length - 1]));78             System.exit(job.waitForCompletion(true) ? 0 : 1);79                 80         }81 82 }
         
        
       
      
     

运行结果：

 

AB      E:C:DAC      E:BAD      B:EAE      C:B:DBC      A:EBD      A:EBE      C:D:ABF      ACD      E:A:BCE      A:BCF      ADE      B:ADF      AEF      A

 

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转自：http://www.aboutyun.com/thread-11107-1-1.html

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