以下是qq的好友列表数据，冒号前是一个用，冒号后是该用户的所有好友（好友关系是单向的，也就是说A是B好友，B不一定是A好友）
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
算出有共同好的的用户?
测试数据
代码
package cn.feizhou.fensi;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;public class SharedFriendsStepOne {static class SharedFriendsStepOneMapper extends Mapper<LongWritable, Text, Text, Text> {@Overrideprotected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {// A:B,C,D,F,E,OString line = value.toString();String[] person_friends = line.split(":");String person = person_friends[0];String friends = person_friends[1];for (String friend : friends.split(",")) {// 输出<好友，人>context.write(new Text(friend), new Text(person));}}}static class SharedFriendsStepOneReducer extends Reducer<Text, Text, Text, Text> {@Overrideprotected void reduce(Text friend, Iterable<Text> 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("H:/test"));FileOutputFormat.setOutputPath(job, new Path("H:/out"));job.waitForCompletion(true);}}
测试结果
