MapReduce—案例（六）求互粉好友对

题目：

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


A-B 就是一对互粉好友对

标准： 最终的所有结果集中必须包含  一组数据   X-Y  必须有  Y-X  
那么我们就认为 X-Y 就是最终的结果--- 互粉好友对

A-B
B-A

A-C

A-D
D-A

B-E

解题思路：

将数据按照从小到大的顺序形成好友对，作为key值，在reduce里面统计key的值，如果key数目为2，即认为是互为好友对。

package practice1;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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;
/**
 * 求互粉好友对
 * @author potter
 */
public class Practice5 {

	public static void main(String[] args) throws Exception {
		
		Configuration conf = new Configuration();
//		conf.set("fs.defaultFS", "hdfs://potter2:9000");
//		System.setProperty("HADOOP_USER_NAME", "potter");
		FileSystem fs = FileSystem.get(conf);
		
		Job job = Job.getInstance();
		job.setJarByClass(Practice5.class);
		job.setMapperClass(Practice5Mapper.class);
		job.setReducerClass(Practice5Reducer.class);
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(NullWritable.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(NullWritable.class);
		
		Path input = new Path("D:\\practice\\input5\\work5.txt");
		Path output = new Path("D:\\practice\\input5\\output1");
		
		FileInputFormat.setInputPaths(job, input);
		FileOutputFormat.setOutputPath(job, output);
		
		if (fs.exists(output)) {
			fs.delete(output,true);
		}
		boolean isdone = job.waitForCompletion(true);
		System.exit(isdone ? 0 :1);
		
	}
	
	public static class Practice5Mapper extends Mapper<LongWritable, Text, Text, NullWritable>{
		Text text1 = new Text();
		@Override
		protected void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {
			/**
			 * A:B,C,D,F,E,O
			 * B:A,C,E,K
			 * C:F,A,D,I
			 */
			String[] split1 = value.toString().trim().split(":");
			String cc = split1[0];
			String[] split2 = split1[1].split(",");
			//用来判断好友对的个数，如果个数等于2，则两个互粉
			for (int i = 0; i < split2.length; i++) {
				String xx = split2[i];
				if (cc.compareTo(xx) < 0) {
					text1.set(cc+"-"+xx);
				}else {
					text1.set(xx+"-"+cc);
				}
				context.write(text1, NullWritable.get());
			}
		}
	}
	
	public static class Practice5Reducer extends Reducer<Text, NullWritable, Text, NullWritable>{
		@Override
		protected void reduce(Text key, Iterable<NullWritable> values, Context context)
				throws IOException, InterruptedException {
			//用来记录好友互粉的个数
			int count = 0;
			for(NullWritable dd : values){
				count++;
			}
			
			if (count == 2) {
				context.write(key, NullWritable.get());
			}
			
		}
	}
}

结果：共16对

A-B
A-C
A-D
A-F
A-O
B-E
C-F
D-E
D-F
D-L
E-L
E-M
F-M
H-O
I-O
J-O