MR求两个用户的共同粉丝列表
以下是qq的好友列表数据，冒号前是一个用户，冒号后是该用户的所有好友（数据中的好友关系是单向的）
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
求出哪些人两两之间有共同好友，及他俩的共同好友都有谁？
解题思路：
第一步
map
读一行 A:B,C,D,F,E,O
输出
package com.ljt.mrsharefriends;
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;
/***
*
* Title: 共同粉丝列表
* 功能描述::
* 1）找出所有用户是哪些用户的共同粉丝
* 2）找出两个用户之间的共同粉丝
*
* Company: adteach
* @author 刘建涛 *
* @date 2017年7月19日下午6:50:39
* @version 1.0
*/
public class SharedFriendsStepOne {
static class SharedFriendsStepOneMapper extends Mapper<LongWritable, Text, Text, Text>{
@Override
protected void map(LongWritable key, Text value, Mapper.Context context)
throws IOException, InterruptedException {
//A:B,C,D,F,E,O
// B:A,C,E,K
String line = value.toString();
//每个用户的粉丝列表
String[] person_friends = line.split(":");
String user = person_friends[0];
String friends = person_friends[1];
for (String friend : friends.split(",")) {
//map输出用户的粉丝<粉丝，用户>给reduce
context.write(new Text(friend), new Text(user));
}
}
}
static class SharedFriendsStepOneReducer extends Reducer<Text, Text, Text, Text> {
@Override
protected void reduce(Text friend, Iterable persons, Context context) throws IOException, InterruptedException {
StringBuffer sb = new StringBuffer();
for (Text person : persons) {
sb.append(person).append(",");
}
context.write(friend, new Text(sb.toString()));
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(SharedFriendsStepOne.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.setMapperClass(SharedFriendsStepOneMapper.class);
job.setReducerClass(SharedFriendsStepOneReducer.class);
FileInputFormat.setInputPaths(job, new Path("srcdata/friends"));
FileOutputFormat.setOutputPath(job, new Path("temp/out"));
job.waitForCompletion(true);
}
}
第二步：找出 <人-人，好友> ，这样，相同的“人-人”对的所有好友就会到同1个reduce中去
package com.ljt.mrsharefriends;
import java.io.IOException;
import java.util.Arrays;
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;
/**
*
* Title: 找出两个用户之间的共同好友
* 功能描述::
* Company: adteach
* @author 刘建涛 *
* @date 2017年7月19日下午7:15:16
* @version 1.0
*/
public class SharedFriendsStepTwo {
static class SharedFriendsStepTwoMapper extends Mapper<LongWritable, Text, Text, Text> {
// 拿到的数据是上一个步骤的输出结果
// A I,K,C,B,G,F,H,O,D,
// 友 人，人，人
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
String[] friend_persons = line.split("\t");
String friend = friend_persons[0];
String[] persons = friend_persons[1].split(",");
//对用户排序
Arrays.sort(persons);
for (int i = 0; i < persons.length - 1; i++) {
for (int j = i + 1; j < persons.length; j++) {
// 发出 <人-人，好友> ，这样，相同的“人-人”对的所有好友就会到同1个reduce中去
context.write(new Text(persons[i] + "-" + persons[j]), new Text(friend));
}
}
}
}
static class SharedFriendsStepTwoReducer extends Reducer<Text, Text, Text, Text> {
@Override
protected void reduce(Text person_person, Iterable friends, Context context) throws IOException, InterruptedException {
StringBuffer sb = new StringBuffer();
for (Text friend : friends) {
sb.append(friend).append(" ");
}
context.write(person_person, new Text(sb.toString()));
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);
job.setJarByClass(SharedFriendsStepTwo.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.setMapperClass(SharedFriendsStepTwoMapper.class);
job.setReducerClass(SharedFriendsStepTwoReducer.class);
FileInputFormat.setInputPaths(job, new Path("/temp/out/part-r-00000"));
FileOutputFormat.setOutputPath(job, new Path("/temp/out2"));
job.waitForCompletion(true);
}
}