转载：MapReduce--求哪些人两两之间是互粉好友

原文链接：https://www.cnblogs.com/break-lian/p/9780133.html

MapReduce--求哪些人两两之间是互粉好友

数据：

A:B,C,D,F,E,O B:A,C,E,K C:F,A,D,I D:A,E,F,L E:B,C,D,M,L F:A,B,C,D,E,O,M G:A,C,D,E,F H:A,C,D,E,O I:A,O J:B,O K:A,C,D L:D,E,F M:E,F,G O:A,H,I,J,K

求哪些人两两之间是互粉好友，形如：A的好友有B，B的好友有A 。 那么A和B就是互粉好友。

思路：

对每一行数据进行组合输出 （person-person，1），

然后再Reducer阶段进行统计，等于2的就是互粉好友对；

问题：将B-A转换成A-B这种形式；

方案：比较两个字符之间的大小，小的在前；

import java.io.IOException;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.NullWritable;
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 EachOtherFriend {public static class MyMapper extends Mapper<LongWritable, Text, Text, IntWritable>{@Overrideprotected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {String[] lines = value.toString().split(":");char person = lines[0].charAt(0); for (String str : lines[1].split(",")) {char friend = str.charAt(0);String per_per = "";if(person > friend){per_per += friend+"-"+person;}else{per_per += person+"-"+friend;}context.write(new Text(per_per), new IntWritable(1));}}}public static class MyReducer extends Reducer<Text, IntWritable, Text, NullWritable>{@Overrideprotected void reduce(Text key, Iterable<IntWritable> values,Context context)throws IOException, InterruptedException {int num = 0;for (IntWritable it : values) {num++;}if(num > 1){context.write(key, null);}}}public static void main(String[] args) throws Exception {Configuration conf = new Configuration();Job job = Job.getInstance(conf);job.setJarByClass(EachOtherFriend.class);job.setMapperClass(MyMapper.class);job.setReducerClass(MyReducer.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(IntWritable.class);job.setOutputKeyClass(Text.class);job.setOutputValueClass(NullWritable.class);FileInputFormat.setInputPaths(job, new Path("G:/files/input"));FileOutputFormat.setOutputPath(job, new Path("G:/files/output"));boolean isDone = job.waitForCompletion(true);System.exit(isDone ? 0:1);}
}