网上好多好推荐之类的博客都是基于二度好友的推荐，下面介绍基于邻接表的好友推荐。
输入：
1 2,3,4,5,6,7,8 2 1,3,4,5,7 3 1,2 4 1,2,6 5 1,2 6 1,4 7 1,2 8 1
第一列表示用户，后面的表示用户的所有好友。
需求：找出用户好友的好友且与用户不是好友的，推荐给用户。
思路：1、key为user，value可设计成user有关联关系的人及关联关系的说明，例如：
key："1" value：<"2", "yes"> 表示"1"与"2"已经是好友关系
key："2" value：<"3", "1">表示"2"与"3"共同的好友为"1"
2、对reduce后的key的value做归类，比如把key为"2"的value的第一个值为"3"的value归为一组，这一组value中的第二个值若没有"yes"出现，则把"3"推荐给"2"，若有"yes"出现，说明"2"与"3"已为好友关系。
步骤：1、map：读取每行数据，组合user与每一个好友，两两组合user的好友。
2、reduce：分析value的第一个值是否时key好友，若不是则可以推荐给key。
package hadoop;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.Collection;
import java.util.Set;
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.Text;
import org.apache.hadoop.io.WritableComparable;
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;
import org.apache.hadoop.util.GenericOptionsParser;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.Multimap;
public class FriendRecom {
static class ValuePair implements WritableComparable<ValuePair> {
private String friend;
private String union;//连结关系
public String getFriend() {
return friend;
}
public void setFriend(String friend) {
this.friend = friend;
}
public String getUnion() {
return union;
}
public void setUnion(String union) {
this.union = union;
}
public ValuePair() {
// TODO Auto-generated constructor stub
}
public ValuePair(String n, String u) {
this.friend = n;
this.union = u;
}
@Override
public void readFields(DataInput in) throws IOException {
this.friend = in.readUTF();
this.union = in.readUTF();
}
@Override
public void write(DataOutput out) throws IOException {
out.writeUTF(this.friend);
out.writeUTF(this.union);
}
@Override
public int compareTo(ValuePair o) {
if (this.friend.equals(o.getFriend())) {
return this.union.compareTo(o.getUnion());
} else {
return this.friend.compareTo(o.getFriend());
}
}
}
static class Map extends Mapper<LongWritable, Text, Text, ValuePair> {
private Text outkey = new Text();
private ValuePair outvalue = new ValuePair();
protected void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
String input = value.toString();
String[] sz = input.split(" ");
this.outkey.set(sz[0]);
String[] sz1 = sz[1].split(",");
for (int i = 0; i < sz1.length; i++) {
this.outvalue.setFriend(sz1[i]);
this.outvalue.setUnion("yes"); //yes表示key与outvalue.friend已经为好友关系
context.write(this.outkey, this.outvalue);
}
for (int i = 0; i < sz1.length; i++) {
for (int j = i + 1; j < sz1.length; j++) {
this.outkey.set(sz1[i]);
this.outvalue.setFriend(sz1[j]);
this.outvalue.setUnion(sz[0]); //表示key与outvalue.friend共同的好友
context.write(this.outkey, this.outvalue);
this.outkey.set(sz1[j]);
this.outvalue.setFriend(sz1[i]);
context.write(this.outkey, this.outvalue);
}
}
}
}
static class Reduce extends Reducer<Text, ValuePair, Text, Text> {
private Text outKey = new Text();
private Text outValue = new Text();
@Override
protected void reduce(Text key, Iterable<ValuePair> values,
Context context) throws IOException, InterruptedException {
this.outKey = key;
Multimap<String, String> map = HashMultimap.create();
for (ValuePair v : values) {
//归约所有与key相关联的人及与key的关联关系
map.put(v.getFriend(), v.getUnion());
// String tmp = v.getFriend() + " " + v.getUnion();
// this.outValue.set(tmp);
// context.write(this.outKey, this.outValue);
}
StringBuilder outString = new StringBuilder();//用来保存输出值
Set<String> keys = map.keySet();//取得所有与key有关的人
for(String s : keys){
StringBuilder outStr = new StringBuilder();
boolean isok = true;//标志是否与key是好友关系
int acc = 0;
Collection<String> v = map.get(s);//v表示与key的关系：yes或共同好友
outStr.append(s + " " + "(");//s表示关联人
String tmp = new String();//用来存放key和s的共同好友
for(String u : v){
if(u.equals("yes")){//表示key与s已经是好友关系了
isok = false;
break;//推出该循环，不推荐s
}
tmp += u + ", ";//记录key与s的共同好友
}
if(tmp.length()>2){//去除tmp结尾的”， “
tmp = tmp.substring(0, tmp.length()-2);
}
if(isok){
outStr.append(v.size() + ": " + "[" + tmp.trim() + "])");
outString.append(outStr);
}
}
outValue.set(outString.toString());
context.write(outKey, outValue);
}
}
private static String inputPath = "in-friend";
private static String outputPath = "out-friend";
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args)
.getRemainingArgs();
Job job = new Job(conf, "friend recomment");
job.setJarByClass(FriendRecom.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
// job.setPartitionerClass(Prt.class);
// job.setNumReduceTasks(6);
// job.setGroupingComparatorClass(Grp.class);
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(ValuePair.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
FileSystem fs = FileSystem.get(conf);
Path inPath = new Path(inputPath);
if (fs.exists(inPath)) {
FileInputFormat.addInputPath(job, inPath);
}
Path outPath = new Path(outputPath);
fs.delete(outPath, true);
FileOutputFormat.setOutputPath(job, outPath);
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
输出：
1 2 6 (2: [4, 1])8 (1: [1]) 3 4 (2: [1, 2])5 (2: [1, 2])6 (1: [1])7 (2: [1, 2])8 (1: [1]) 4 3 (2: [1, 2])5 (2: [1, 2])7 (2: [1, 2])8 (1: [1]) 5 3 (2: [1, 2])4 (2: [1, 2])6 (1: [1])7 (2: [1, 2])8 (1: [1]) 6 2 (2: [4, 1])3 (1: [1])5 (1: [1])7 (1: [1])8 (1: [1]) 7 3 (2: [1, 2])4 (2: [1, 2])5 (2: [1, 2])6 (1: [1])8 (1: [1]) 8 2 (1: [1])3 (1: [1])4 (1: [1])5 (1: [1])6 (1: [1])7 (1: [1])