Hadoop/MapReduce 共同好友解决方案：求大量集合的两两交集

共同好友:求大量集合的两两交集
目标：令U为包含所有用户的一个集合:{U1,U2,...,Un}，我们的目标是为每个(Ui,Uj)对(i!=j)找出共同好友。
前提:好友关系是双向的

输入:<person><,><friend1>< ><friend2>< >...<friendN>

100,200 300 400 500 600
200,100 300 400
300,100 200 400 500
400,100 200 300
500,100,300
600,100

解决方案1：POJO共同好友解决方案
令{A1,A2,...,Am}是用户User1的好友集合，{B1,B2,...,B}是用户User2的好友集合。因此
User1和User2的共同好友可以定义为两个集合的交集（共同元素）。

public static Set<Integer> intersection(Set<Integer> user1friends,Set<Integer> user2friends)
{
if(user1friends == null || user2friends == null)
return null;
if(user1friends.isEmpty() || user2friends.isEmpty())
return null;
if(user1friends.size() < user2friends.size())
return intersect(user1friends,user2friends);
else
return intersect(user2friends,user1friends);
}

public static Set<Integer> intersect(Set<Integer> small,Set<Integer> large)
{
Set<Integer> result = new TreeSet<Integer>();
for(Integer x : small)//迭代器处理小集合以提高性能
{
if(large.contains(x))
result.add(x);
}
}

解决方案2：Hadoop/MapReduce实现

思路：
对于100 200 300 400 500 600，生成
([100,200],[200 300 400 500 600])，意为用户100和用户200中有一方的好友列表为[200 300 400 500 600]--------（1）
([100,300],[200 300 400 500 600])，意为用户100和用户300中有一方的好友列表为[200 300 400 500 600]
([100,400],[200 300 400 500 600])，意为用户100和用户400中有一方的好友列表为[200 300 400 500 600]
([100,500],[200 300 400 500 600])，意为用户100和用户50中有一方的好友列表为[200 300 400 500 600]
([100,600],[200 300 400 500 600])，意为用户100和用户600中有一方的好友列表为[200 300 400 500 600]
对于200 100 300 400，生成
([100,200],[100 300 400]),意为用户100和用户200中有一方的好友列表为[100 300 400]--------------------------(2)
([200,300],[100 300 400]),意为用户200和用户300中有一方的好友列表为[100 300 400]
([200,400],[100 300 400]),意为用户200和用户400中有一方的好友列表为[100 300 400]
...
然后按照键进行规约，例如，(1)和(2)会到达同一个规约器
([100,200],([200 300 400 500 600],[100 300 400])
只需要求两个集合的交集即可：
维护一个<String,Integer>的map，统计各个集合各个元素的出现次数
(100,1)
(200,1)
(300,2)
(400,2)
(500,1)
(600,1)
遍历map找出出现2次的键:300 400
加入结果的值中，输出([100,200],[300 400])

实现1：生成类似([100,200],[200 300 400 500 600])的键值对时使用Text保存[200 300 400 500 600]

package commonfriends;import java.io.IOException;import org.apache.hadoop.io.Text;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.mapreduce.Mapper;import org.apache.commons.lang.StringUtils;public class CommonFriendsMapperextends Mapper<LongWritable, Text, Text, Text> {private static final Text REDUCER_KEY = new Text();private static final Text REDUCER_VALUE = new Text();static String getFriends(String[] tokens) {if (tokens.length == 2) {return "";}StringBuilder builder = new StringBuilder();for (int i = 1; i < tokens.length; i++) {builder.append(tokens[i]);if (i < (tokens.length - 1)) {builder.append(",");}}return builder.toString();}static String buildSortedKey(String person, String friend) {long p = Long.parseLong(person);long f = Long.parseLong(friend);if (p < f) {return person + "," + friend;} else {return friend + "," + person;}}public void map(LongWritable key, Text value, Context context)throws IOException, InterruptedException {// parse input, delimiter is a single spaceString[] tokens = StringUtils.split(value.toString(), " ");// create reducer valueString friends = getFriends(tokens);REDUCER_VALUE.set(friends);String person = tokens[0];for (int i = 1; i < tokens.length; i++) {String friend = tokens[i];String reducerKeyAsString = buildSortedKey(person, friend);REDUCER_KEY.set(reducerKeyAsString);context.write(REDUCER_KEY, REDUCER_VALUE);}}}

package commonfriends;import java.util.Map;import java.util.HashMap;import java.util.List;import java.util.ArrayList;import java.util.Iterator;import java.io.IOException;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;import org.apache.commons.lang.StringUtils;public class CommonFriendsReducer extends Reducer<Text, Text, Text, Text> {@Overridepublic void reduce(Text key, Iterable<Text> values, Context context)throws IOException, InterruptedException {System.out.println("key=" + key);Map<String, Integer> map = new HashMap<String, Integer>();Iterator<Text> iterator = values.iterator();int numOfValues = 0;while (iterator.hasNext()) {String friends = iterator.next().toString();System.out.println("friends =" + friends);if (friends.equals("")) {context.write(key, new Text("[]"));return;}addFriends(map, friends);numOfValues++;}// now iterate the map to see how many have numOfValuesList<String> commonFriends = new ArrayList<String>();for (Map.Entry<String, Integer> entry : map.entrySet()) {//System.out.println(entry.getKey() + "/" + entry.getValue());if (entry.getValue() == numOfValues) {commonFriends.add(entry.getKey());}}// sen it to outputcontext.write(key, new Text(commonFriends.toString()));}static void addFriends(Map<String, Integer> map, String friendsList) {String[] friends = StringUtils.split(friendsList, ",");for (String friend : friends) {Integer count = map.get(friend);if (count == null) {map.put(friend, 1);} else {map.put(friend, ++count);}}}}

package commonfriends;import org.apache.log4j.Logger;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.conf.Configured;import org.apache.hadoop.util.Tool;import org.apache.hadoop.util.ToolRunner;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.Text;public class CommonFriendsDriver extends Configured implements Tool {private static final Logger theLogger = Logger.getLogger(CommonFriendsDriver.class);@Overridepublic int run(String[] args) throws Exception {Job job = new Job(getConf());job.setJobName("CommonFriendsDriver");// add jars to distributed cache//HadoopUtil.addJarsToDistributedCache(job, "/lib/");job.setInputFormatClass(TextInputFormat.class);job.setOutputFormatClass(TextOutputFormat.class);job.setOutputKeyClass(Text.class);			// mapper will generate key as Text (the keys are as (person1,person2))job.setOutputValueClass(Text.class);		// mapper will generate value as Text (list of friends)job.setMapperClass(CommonFriendsMapper.class);job.setReducerClass(CommonFriendsReducer.class);// args[0] = input directory// args[1] = output directoryFileInputFormat.setInputPaths(job, new Path(args[0]));FileOutputFormat.setOutputPath(job, new Path(args[1]));boolean status = job.waitForCompletion(true);theLogger.info("run(): status=" + status);return status ? 0 : 1;}/*** The main driver for word count map/reduce program. Invoke this method to submit the map/reduce job.** @throws Exception When there is communication problems with the job tracker.*/public static void main(String[] args) throws Exception {args = new String[2];args[0] = "input/friends.txt";args[1] = "output/friends1";// Make sure there are exactly 2 parametersif (args.length != 2) {throw new IllegalArgumentException("usage: Argument 1: input dir, Argument 2: output dir");}theLogger.info("inputDir=" + args[0]);theLogger.info("outputDir=" + args[1]);int jobStatus = submitJob(args);theLogger.info("jobStatus=" + jobStatus);System.exit(jobStatus);}/*** The main driver for word count map/reduce program. Invoke this method to submit the map/reduce job.** @throws Exception When there is communication problems with the job tracker.*/public static int submitJob(String[] args) throws Exception {int jobStatus = ToolRunner.run(new CommonFriendsDriver(), args);return jobStatus;}}

实现2:生成类似([100,200],[200 300 400 500 600])的键值对时使用ArrayListOfLongsWritable保存[200 300 400 500 600]

package commonfriends;import java.io.IOException;import org.apache.hadoop.io.Text;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.mapreduce.Mapper;import org.apache.commons.lang.StringUtils;import edu.umd.cloud9.io.array.ArrayListOfLongsWritable;public class CommonFriendsMapperUsingListextends Mapper<LongWritable, Text, Text, ArrayListOfLongsWritable> {private static final Text REDUCER_KEY = new Text();static ArrayListOfLongsWritable getFriends(String[] tokens) {if (tokens.length == 2) {return new ArrayListOfLongsWritable();}ArrayListOfLongsWritable list = new ArrayListOfLongsWritable();for (int i = 1; i < tokens.length; i++) {list.add(Long.parseLong(tokens[i]));}return list;}static String buildSortedKey(String person, String friend) {long p = Long.parseLong(person);long f = Long.parseLong(friend);if (p < f) {return person + "," + friend;} else {return friend + "," + person;}}@Overridepublic void map(LongWritable key, Text value, Context context)throws IOException, InterruptedException {// parse input, delimiter is a single spaceString[] tokens = StringUtils.split(value.toString(), " ");// create reducer valueArrayListOfLongsWritable friends = getFriends(tokens);String person = tokens[0];for (int i = 1; i < tokens.length; i++) {String friend = tokens[i];String reducerKeyAsString = buildSortedKey(person, friend);REDUCER_KEY.set(reducerKeyAsString);context.write(REDUCER_KEY, friends);}}}

package commonfriends;import java.util.Map;import java.util.HashMap;import java.util.List;import java.util.ArrayList;import java.util.Iterator;import java.io.IOException;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;import edu.umd.cloud9.io.array.ArrayListOfLongsWritable;public class CommonFriendsReducerUsingListextends Reducer<Text, ArrayListOfLongsWritable, Text, Text> {@Overridepublic void reduce(Text key, Iterable<ArrayListOfLongsWritable> values, Context context)throws IOException, InterruptedException {// map<k, v> where k is userID, and v is the countMap<Long, Integer> map = new HashMap<Long, Integer>();Iterator<ArrayListOfLongsWritable> iterator = values.iterator();int numOfValues = 0;while (iterator.hasNext()) {ArrayListOfLongsWritable friends = iterator.next();if (friends == null) {context.write(key, null);return;}addFriends(map, friends);numOfValues++;}// now iterate the map to see how many have numOfValuesList<Long> commonFriends = new ArrayList<Long>();for (Map.Entry<Long, Integer> entry : map.entrySet()) {//System.out.println(entry.getKey() + "/" + entry.getValue());if (entry.getValue() == numOfValues) {commonFriends.add(entry.getKey());}}// sen it to outputcontext.write(key, new Text(commonFriends.toString()));}static void addFriends(Map<Long, Integer> map, ArrayListOfLongsWritable friendsList) {Iterator<Long> iterator = friendsList.iterator();while (iterator.hasNext()) {long id = iterator.next();Integer count = map.get(id);if (count == null) {map.put(id, 1);} else {map.put(id, ++count);}}}}

package commonfriends;import org.apache.log4j.Logger;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.conf.Configured;import org.apache.hadoop.util.Tool;import org.apache.hadoop.util.ToolRunner;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.Text;import edu.umd.cloud9.io.array.ArrayListOfLongsWritable;public class CommonFriendsDriverUsingList  extends Configured implements Tool {private static Logger theLogger = Logger.getLogger(CommonFriendsDriverUsingList.class);public int run(String[] args) throws Exception {Job job = new Job(getConf());job.setJobName("CommonFriendsDriverUsingList");// add jars to distributed cache//HadoopUtil.addJarsToDistributedCache(job, "/lib/");job.setInputFormatClass(TextInputFormat.class);job.setOutputFormatClass(TextOutputFormat.class);// mapper will generate key as Text (the keys are as (person1,person2))job.setOutputKeyClass(Text.class);// mapper will generate value as ArrayListOfLongsWritable (list of friends)job.setOutputValueClass(ArrayListOfLongsWritable.class);job.setMapperClass(CommonFriendsMapperUsingList.class);job.setReducerClass(CommonFriendsReducerUsingList.class);// args[0] = input directory// args[1] = output directoryFileInputFormat.setInputPaths(job, new Path(args[0]));FileOutputFormat.setOutputPath(job, new Path(args[1]));boolean status = job.waitForCompletion(true);theLogger.info("run(): status="+status);return status ? 0 : 1;}/*** The main driver for word count map/reduce program.* Invoke this method to submit the map/reduce job.* @throws Exception When there is communication problems with the job tracker.*/public static void main(String[] args) throws Exception {// Make sure there are exactly 2 parametersif (args.length != 2) {throw new IllegalArgumentException("usage: Argument 1: input dir, Argument 2: output dir");}theLogger.info("inputDir="+args[0]);theLogger.info("outputDir="+args[1]);int jobStatus = submitJob(args);theLogger.info("jobStatus="+jobStatus);System.exit(jobStatus);}/*** The main driver for word count map/reduce program.* Invoke this method to submit the map/reduce job.* @throws Exception When there is communication problems with the job tracker.*/public static int submitJob(String[] args) throws Exception {int jobStatus = ToolRunner.run(new CommonFriendsDriverUsingList(), args);return jobStatus;}}

结果：100,200    [300, 400]100,300    [200, 400, 500]100,400    [200, 300]100,500    [300]100,600    []200,300    [100, 400]200,400    [100, 300]300,400    [100, 200]300,500    [100]