用Hadoop构建电影推荐系统

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hadoop-recommand

前言

Netflix电影推荐的百万美金比赛，把“推荐”变成了时下最热门的数据挖掘算法之一。也正是由于Netflix的比赛，让企业界和学科界有了更深层次的技术碰撞。引发了各种网站“推荐”热，个性时代已经到来。

目录

  1. 推荐系统概述
  2. 需求分析：推荐系统指标设计
  3. 算法模型：Hadoop并行算法
  4. 架构设计：推荐系统架构
  5. 程序开发：MapReduce程序实现
  6. 补充内容：对Step4过程优化

1. 推荐系统概述

电子商务网站是个性化推荐系统重要地应用的领域之一，亚马逊就是个性化推荐系统的积极应用者和推广者，亚马逊的推荐系统深入到网站的各类商品，为亚马逊带来了至少30%的销售额。

不光是电商类，推荐系统无处不在。QQ，人人网的好友推荐；新浪微博的你可能感觉兴趣的人；优酷，土豆的电影推荐；豆瓣的图书推荐；大从点评的餐饮推荐；世纪佳缘的相亲推荐；天际网的职业推荐等。

推荐算法分类：

按数据使用划分：

  • 协同过滤算法：UserCF, ItemCF, ModelCF
  • 基于内容的推荐: 用户内容属性和物品内容属性
  • 社会化过滤：基于用户的社会网络关系

按模型划分：

  • 最近邻模型:基于距离的协同过滤算法
  • Latent Factor Mode(SVD)：基于矩阵分解的模型
  • Graph：图模型，社会网络图模型

基于用户的协同过滤算法UserCF

基于用户的协同过滤，通过不同用户对物品的评分来评测用户之间的相似性，基于用户之间的相似性做出推荐。简单来讲就是：给用户推荐和他兴趣相似的其他用户喜欢的物品。

用例说明：

image015

算法实现及使用介绍，请参考文章：Mahout推荐算法API详解

基于物品的协同过滤算法ItemCF

基于item的协同过滤，通过用户对不同item的评分来评测item之间的相似性，基于item之间的相似性做出推荐。简单来讲就是：给用户推荐和他之前喜欢的物品相似的物品。

用例说明：

image017


算法实现及使用介绍，请参考文章：Mahout推荐算法API详解

注：基于物品的协同过滤算法，是目前商用最广泛的推荐算法。

协同过滤算法实现，分为2个步骤

  • 1. 计算物品之间的相似度
  • 2. 根据物品的相似度和用户的历史行为给用户生成推荐列表

有关协同过滤的另一篇文章，请参考：RHadoop实践系列之三 R实现MapReduce的协同过滤算法

2. 需求分析：推荐系统指标设计

下面我们将从一个公司案例出发来全面的解释，如何进行推荐系统指标设计。

案例介绍

Netflix电影推荐百万奖金比赛，http://www.netflixprize.com/
Netflix官方网站：www.netflix.com

Netflix，2006年组织比赛是的时候，是一家以在线电影租赁为生的公司。他们根据网友对电影的打分来判断用户有可能喜欢什么电影，并结合会员看过的电影以及口味偏好设置做出判断，混搭出各种电影风格的需求。

收集会员的一些信息，为他们指定个性化的电影推荐后，有许多冷门电影竟然进入了候租榜单。从公司的电影资源成本方面考量，热门电影的成本一般较高，如果Netflix公司能够在电影租赁中增加冷门电影的比例，自然能够提升自身盈利能力。

Netflix公司曾宣称60%左右的会员根据推荐名单定制租赁顺序，如果推荐系统不能准确地猜测会员喜欢的电影类型，容易造成多次租借冷门电影而并不符合个人口味的会员流失。为了更高效地为会员推荐电影，Netflix一直致力于不断改进和完善个性化推荐服务，在2006年推出百万美元大奖，无论是谁能最好地优化Netflix推荐算法就可获奖励100万美元。到2009年，奖金被一个7人开发小组夺得，Netflix随后又立即推出第二个百万美金悬赏。这充分说明一套好的推荐算法系统是多么重要，同时又是多么困难。

netflix_prize

上图为比赛的各支队伍的排名！

补充说明：

  • 1. Netflix的比赛是基于静态数据的，就是给定“训练级”，匹配“结果集”，“结果集”也是提前就做好的，所以这与我们每天运营的系统，其实是不一样的。
  • 2. Netflix用于比赛的数据集是小量的，整个全集才666MB，而实际的推荐系统都要基于大量历史数据的，动不动就会上GB,TB等

Netflix数据下载
部分训练集：http://graphlab.org/wp-content/uploads/2013/07/smallnetflix_mm.train_.gz
部分结果集：http://graphlab.org/wp-content/uploads/2013/07/smallnetflix_mm.validate.gz
完整数据集：http://www.lifecrunch.biz/wp-content/uploads/2011/04/nf_prize_dataset.tar.gz

所以，我们在真实的环境中设计推荐的时候，要全面考量数据量，算法性能，结果准确度等的指标。

  • 推荐算法选型：基于物品的协同过滤算法ItemCF，并行实现
  • 数据量：基于Hadoop架构，支持GB,TB,PB级数据量
  • 算法检验：可以通过 准确率，召回率，覆盖率，流行度 等指标评判。
  • 结果解读：通过ItemCF的定义，合理给出结果解释

3. 算法模型：Hadoop并行算法

这里我使用”Mahout In Action”书里，第一章第六节介绍的分步式基于物品的协同过滤算法进行实现。Chapter 6: Distributing recommendation computations

测试数据集:small.csv



1,101,5.0

1,102,3.0

1,103,2.5

2,101,2.0

2,102,2.5

2,103,5.0

2,104,2.0

3,101,2.0

3,104,4.0

3,105,4.5

3,107,5.0

4,101,5.0

4,103,3.0

4,104,4.5

4,106,4.0

5,101,4.0

5,102,3.0

5,103,2.0

5,104,4.0

5,105,3.5

5,106,4.0

每行3个字段，依次是用户ID,电影ID,用户对电影的评分(0-5分，每0.5为一个评分点！)

算法的思想：

  • 1. 建立物品的同现矩阵
  • 2. 建立用户对物品的评分矩阵
  • 3. 矩阵计算推荐结果

1). 建立物品的同现矩阵
按用户分组，找到每个用户所选的物品，单独出现计数及两两一组计数。



      [101] [102] [103] [104] [105] [106] [107]

[101]   5     3     4     4     2     2     1

[102]   3     3     3     2     1     1     0

[103]   4     3     4     3     1     2     0

[104]   4     2     3     4     2     2     1

[105]   2     1     1     2     2     1     1

[106]   2     1     2     2     1     2     0

[107]   1     0     0     1     1     0     1

2). 建立用户对物品的评分矩阵
按用户分组，找到每个用户所选的物品及评分



       U3

[101] 2.0

[102] 0.0

[103] 0.0

[104] 4.0

[105] 4.5

[106] 0.0

[107] 5.0

3). 矩阵计算推荐结果
同现矩阵*评分矩阵=推荐结果

alogrithm_1


图片摘自”Mahout In Action”

MapReduce任务设计


aglorithm_2

图片摘自”Mahout In Action”

解读MapRduce任务：

  • 步骤1: 按用户分组，计算所有物品出现的组合列表，得到用户对物品的评分矩阵
  • 步骤2: 对物品组合列表进行计数，建立物品的同现矩阵
  • 步骤3: 合并同现矩阵和评分矩阵
  • 步骤4: 计算推荐结果列表

4. 架构设计：推荐系统架构

hadoop-recommand-architect


上图中，左边是Application业务系统，右边是Hadoop的HDFS, MapReduce。

  1. 业务系统记录了用户的行为和对物品的打分
  2. 设置系统定时器CRON，每xx小时，增量向HDFS导入数据(userid,itemid,value,time)。
  3. 完成导入后，设置系统定时器，启动MapReduce程序，运行推荐算法。
  4. 完成计算后，设置系统定时器，从HDFS导出推荐结果数据到数据库，方便以后的及时查询。

5. 程序开发：MapReduce程序实现

win7的开发环境 和 Hadoop的运行环境 ，请参考文章：用Maven构建Hadoop项目

新建Java类：

  • Recommend.java，主任务启动程序
  • Step1.java，按用户分组，计算所有物品出现的组合列表，得到用户对物品的评分矩阵
  • Step2.java，对物品组合列表进行计数，建立物品的同现矩阵
  • Step3.java，合并同现矩阵和评分矩阵
  • Step4.java，计算推荐结果列表
  • HdfsDAO.java，HDFS操作工具类

1). Recommend.java，主任务启动程序
源代码：



package org.conan.myhadoop.recommend;



import java.util.HashMap;

import java.util.Map;

import java.util.regex.Pattern;



import org.apache.hadoop.mapred.JobConf;



public class Recommend {



    public static final String HDFS = "hdfs://192.168.1.210:9000";

    public static final Pattern DELIMITER = Pattern.compile("[\t,]");



    public static void main(String[] args) throws Exception {

        Map<String, String> path = new HashMap<String, String>();

        path.put("data", "logfile/small.csv");

        path.put("Step1Input", HDFS + "/user/hdfs/recommend");

        path.put("Step1Output", path.get("Step1Input") + "/step1");

        path.put("Step2Input", path.get("Step1Output"));

        path.put("Step2Output", path.get("Step1Input") + "/step2");

        path.put("Step3Input1", path.get("Step1Output"));

        path.put("Step3Output1", path.get("Step1Input") + "/step3_1");

        path.put("Step3Input2", path.get("Step2Output"));

        path.put("Step3Output2", path.get("Step1Input") + "/step3_2");

        path.put("Step4Input1", path.get("Step3Output1"));

        path.put("Step4Input2", path.get("Step3Output2"));

        path.put("Step4Output", path.get("Step1Input") + "/step4");



        Step1.run(path);

        Step2.run(path);

        Step3.run1(path);

        Step3.run2(path);

        Step4.run(path);

        System.exit(0);

    }



    public static JobConf config() {

        JobConf conf = new JobConf(Recommend.class);

        conf.setJobName("Recommend");

        conf.addResource("classpath:/hadoop/core-site.xml");

        conf.addResource("classpath:/hadoop/hdfs-site.xml");

        conf.addResource("classpath:/hadoop/mapred-site.xml");

        return conf;

    }



}

2). Step1.java，按用户分组，计算所有物品出现的组合列表，得到用户对物品的评分矩阵

源代码：



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.Iterator;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.FileInputFormat;

import org.apache.hadoop.mapred.FileOutputFormat;

import org.apache.hadoop.mapred.JobClient;

import org.apache.hadoop.mapred.JobConf;

import org.apache.hadoop.mapred.MapReduceBase;

import org.apache.hadoop.mapred.Mapper;

import org.apache.hadoop.mapred.OutputCollector;

import org.apache.hadoop.mapred.Reducer;

import org.apache.hadoop.mapred.Reporter;

import org.apache.hadoop.mapred.RunningJob;

import org.apache.hadoop.mapred.TextInputFormat;

import org.apache.hadoop.mapred.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step1 {



    public static class Step1_ToItemPreMapper extends MapReduceBase implements Mapper<Object, Text, IntWritable, Text> {

        private final static IntWritable k = new IntWritable();

        private final static Text v = new Text();



        @Override

        public void map(Object key, Text value, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {

            String[] tokens = Recommend.DELIMITER.split(value.toString());

            int userID = Integer.parseInt(tokens[0]);

            String itemID = tokens[1];

            String pref = tokens[2];

            k.set(userID);

            v.set(itemID + ":" + pref);

            output.collect(k, v);

        }

    }



    public static class Step1_ToUserVectorReducer extends MapReduceBase implements Reducer<IntWritable, Text, IntWritable, Text> {

        private final static Text v = new Text();



        @Override

        public void reduce(IntWritable key, Iterator values, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {

            StringBuilder sb = new StringBuilder();

            while (values.hasNext()) {

                sb.append("," + values.next());

            }

            v.set(sb.toString().replaceFirst(",", ""));

            output.collect(key, v);

        }

    }



    public static void run(Map<String, String> path) throws IOException {

        JobConf conf = Recommend.config();



        String input = path.get("Step1Input");

        String output = path.get("Step1Output");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(input);

        hdfs.mkdirs(input);

        hdfs.copyFile(path.get("data"), input);



        conf.setMapOutputKeyClass(IntWritable.class);

        conf.setMapOutputValueClass(Text.class);



        conf.setOutputKeyClass(IntWritable.class);

        conf.setOutputValueClass(Text.class);



        conf.setMapperClass(Step1_ToItemPreMapper.class);

        conf.setCombinerClass(Step1_ToUserVectorReducer.class);

        conf.setReducerClass(Step1_ToUserVectorReducer.class);



        conf.setInputFormat(TextInputFormat.class);

        conf.setOutputFormat(TextOutputFormat.class);



        FileInputFormat.setInputPaths(conf, new Path(input));

        FileOutputFormat.setOutputPath(conf, new Path(output));



        RunningJob job = JobClient.runJob(conf);

        while (!job.isComplete()) {

            job.waitForCompletion();

        }

    }



}

计算结果：



~ hadoop fs -cat /user/hdfs/recommend/step1/part-00000



1       102:3.0,103:2.5,101:5.0

2       101:2.0,102:2.5,103:5.0,104:2.0

3       107:5.0,101:2.0,104:4.0,105:4.5

4       101:5.0,103:3.0,104:4.5,106:4.0

5       101:4.0,102:3.0,103:2.0,104:4.0,105:3.5,106:4.0

3). Step2.java，对物品组合列表进行计数，建立物品的同现矩阵
源代码：



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.Iterator;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.FileInputFormat;

import org.apache.hadoop.mapred.FileOutputFormat;

import org.apache.hadoop.mapred.JobClient;

import org.apache.hadoop.mapred.JobConf;

import org.apache.hadoop.mapred.MapReduceBase;

import org.apache.hadoop.mapred.Mapper;

import org.apache.hadoop.mapred.OutputCollector;

import org.apache.hadoop.mapred.Reducer;

import org.apache.hadoop.mapred.Reporter;

import org.apache.hadoop.mapred.RunningJob;

import org.apache.hadoop.mapred.TextInputFormat;

import org.apache.hadoop.mapred.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step2 {

    public static class Step2_UserVectorToCooccurrenceMapper extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {

        private final static Text k = new Text();

        private final static IntWritable v = new IntWritable(1);



        @Override

        public void map(LongWritable key, Text values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());

            for (int i = 1; i < tokens.length; i++) {

                String itemID = tokens[i].split(":")[0];

                for (int j = 1; j < tokens.length; j++) {

                    String itemID2 = tokens[j].split(":")[0];

                    k.set(itemID + ":" + itemID2);

                    output.collect(k, v);

                }

            }

        }

    }



    public static class Step2_UserVectorToConoccurrenceReducer extends MapReduceBase implements Reducer<Text, IntWritable, Text, IntWritable> {

        private IntWritable result = new IntWritable();



        @Override

        public void reduce(Text key, Iterator values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {

            int sum = 0;

            while (values.hasNext()) {

                sum += values.next().get();

            }

            result.set(sum);

            output.collect(key, result);

        }

    }



    public static void run(Map<String, String> path) throws IOException {

        JobConf conf = Recommend.config();



        String input = path.get("Step2Input");

        String output = path.get("Step2Output");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        conf.setOutputKeyClass(Text.class);

        conf.setOutputValueClass(IntWritable.class);



        conf.setMapperClass(Step2_UserVectorToCooccurrenceMapper.class);

        conf.setCombinerClass(Step2_UserVectorToConoccurrenceReducer.class);

        conf.setReducerClass(Step2_UserVectorToConoccurrenceReducer.class);



        conf.setInputFormat(TextInputFormat.class);

        conf.setOutputFormat(TextOutputFormat.class);



        FileInputFormat.setInputPaths(conf, new Path(input));

        FileOutputFormat.setOutputPath(conf, new Path(output));



        RunningJob job = JobClient.runJob(conf);

        while (!job.isComplete()) {

            job.waitForCompletion();

        }

    }

}

计算结果：



~ hadoop fs -cat /user/hdfs/recommend/step2/part-00000



101:101 5

101:102 3

101:103 4

101:104 4

101:105 2

101:106 2

101:107 1

102:101 3

102:102 3

102:103 3

102:104 2

102:105 1

102:106 1

103:101 4

103:102 3

103:103 4

103:104 3

103:105 1

103:106 2

104:101 4

104:102 2

104:103 3

104:104 4

104:105 2

104:106 2

104:107 1

105:101 2

105:102 1

105:103 1

105:104 2

105:105 2

105:106 1

105:107 1

106:101 2

106:102 1

106:103 2

106:104 2

106:105 1

106:106 2

107:101 1

107:104 1

107:105 1

107:107 1

4). Step3.java，合并同现矩阵和评分矩阵
源代码：



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.FileInputFormat;

import org.apache.hadoop.mapred.FileOutputFormat;

import org.apache.hadoop.mapred.JobClient;

import org.apache.hadoop.mapred.JobConf;

import org.apache.hadoop.mapred.MapReduceBase;

import org.apache.hadoop.mapred.Mapper;

import org.apache.hadoop.mapred.OutputCollector;

import org.apache.hadoop.mapred.Reporter;

import org.apache.hadoop.mapred.RunningJob;

import org.apache.hadoop.mapred.TextInputFormat;

import org.apache.hadoop.mapred.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step3 {



    public static class Step31_UserVectorSplitterMapper extends MapReduceBase implements Mapper<LongWritable, Text, IntWritable, Text> {

        private final static IntWritable k = new IntWritable();

        private final static Text v = new Text();



        @Override

        public void map(LongWritable key, Text values, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());

            for (int i = 1; i < tokens.length; i++) {

                String[] vector = tokens[i].split(":");

                int itemID = Integer.parseInt(vector[0]);

                String pref = vector[1];



                k.set(itemID);

                v.set(tokens[0] + ":" + pref);

                output.collect(k, v);

            }

        }

    }



    public static void run1(Map<String, String> path) throws IOException {

        JobConf conf = Recommend.config();



        String input = path.get("Step3Input1");

        String output = path.get("Step3Output1");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        conf.setOutputKeyClass(IntWritable.class);

        conf.setOutputValueClass(Text.class);



        conf.setMapperClass(Step31_UserVectorSplitterMapper.class);



        conf.setInputFormat(TextInputFormat.class);

        conf.setOutputFormat(TextOutputFormat.class);



        FileInputFormat.setInputPaths(conf, new Path(input));

        FileOutputFormat.setOutputPath(conf, new Path(output));



        RunningJob job = JobClient.runJob(conf);

        while (!job.isComplete()) {

            job.waitForCompletion();

        }

    }



    public static class Step32_CooccurrenceColumnWrapperMapper extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {

        private final static Text k = new Text();

        private final static IntWritable v = new IntWritable();



        @Override

        public void map(LongWritable key, Text values, OutputCollector<Text, IntWritable> output, Reporter reporter) throws IOException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());

            k.set(tokens[0]);

            v.set(Integer.parseInt(tokens[1]));

            output.collect(k, v);

        }

    }



    public static void run2(Map<String, String> path) throws IOException {

        JobConf conf = Recommend.config();



        String input = path.get("Step3Input2");

        String output = path.get("Step3Output2");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        conf.setOutputKeyClass(Text.class);

        conf.setOutputValueClass(IntWritable.class);



        conf.setMapperClass(Step32_CooccurrenceColumnWrapperMapper.class);



        conf.setInputFormat(TextInputFormat.class);

        conf.setOutputFormat(TextOutputFormat.class);



        FileInputFormat.setInputPaths(conf, new Path(input));

        FileOutputFormat.setOutputPath(conf, new Path(output));



        RunningJob job = JobClient.runJob(conf);

        while (!job.isComplete()) {

            job.waitForCompletion();

        }

    }



}

计算结果：



~ hadoop fs -cat /user/hdfs/recommend/step3_1/part-00000



101     5:4.0

101     1:5.0

101     2:2.0

101     3:2.0

101     4:5.0

102     1:3.0

102     5:3.0

102     2:2.5

103     2:5.0

103     5:2.0

103     1:2.5

103     4:3.0

104     2:2.0

104     5:4.0

104     3:4.0

104     4:4.5

105     3:4.5

105     5:3.5

106     5:4.0

106     4:4.0

107     3:5.0



~ hadoop fs -cat /user/hdfs/recommend/step3_2/part-00000



101:101 5

101:102 3

101:103 4

101:104 4

101:105 2

101:106 2

101:107 1

102:101 3

102:102 3

102:103 3

102:104 2

102:105 1

102:106 1

103:101 4

103:102 3

103:103 4

103:104 3

103:105 1

103:106 2

104:101 4

104:102 2

104:103 3

104:104 4

104:105 2

104:106 2

104:107 1

105:101 2

105:102 1

105:103 1

105:104 2

105:105 2

105:106 1

105:107 1

106:101 2

106:102 1

106:103 2

106:104 2

106:105 1

106:106 2

107:101 1

107:104 1

107:105 1

107:107 1

5). Step4.java，计算推荐结果列表
源代码：



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IntWritable;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.FileInputFormat;

import org.apache.hadoop.mapred.FileOutputFormat;

import org.apache.hadoop.mapred.JobClient;

import org.apache.hadoop.mapred.JobConf;

import org.apache.hadoop.mapred.MapReduceBase;

import org.apache.hadoop.mapred.Mapper;

import org.apache.hadoop.mapred.OutputCollector;

import org.apache.hadoop.mapred.Reducer;

import org.apache.hadoop.mapred.Reporter;

import org.apache.hadoop.mapred.RunningJob;

import org.apache.hadoop.mapred.TextInputFormat;

import org.apache.hadoop.mapred.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step4 {



    public static class Step4_PartialMultiplyMapper extends MapReduceBase implements Mapper<LongWritable, Text, IntWritable, Text> {

        private final static IntWritable k = new IntWritable();

        private final static Text v = new Text();



        private final static Map<Integer, List> cooccurrenceMatrix = new HashMap<Integer, List>();



        @Override

        public void map(LongWritable key, Text values, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());



            String[] v1 = tokens[0].split(":");

            String[] v2 = tokens[1].split(":");



            if (v1.length > 1) {// cooccurrence

                int itemID1 = Integer.parseInt(v1[0]);

                int itemID2 = Integer.parseInt(v1[1]);

                int num = Integer.parseInt(tokens[1]);



                List list = null;

                if (!cooccurrenceMatrix.containsKey(itemID1)) {

                    list = new ArrayList();

                } else {

                    list = cooccurrenceMatrix.get(itemID1);

                }

                list.add(new Cooccurrence(itemID1, itemID2, num));

                cooccurrenceMatrix.put(itemID1, list);

            }



            if (v2.length > 1) {// userVector

                int itemID = Integer.parseInt(tokens[0]);

                int userID = Integer.parseInt(v2[0]);

                double pref = Double.parseDouble(v2[1]);

                k.set(userID);

                for (Cooccurrence co : cooccurrenceMatrix.get(itemID)) {

                    v.set(co.getItemID2() + "," + pref * co.getNum());

                    output.collect(k, v);

                }



            }

        }

    }



    public static class Step4_AggregateAndRecommendReducer extends MapReduceBase implements Reducer<IntWritable, Text, IntWritable, Text> {

        private final static Text v = new Text();



        @Override

        public void reduce(IntWritable key, Iterator values, OutputCollector<IntWritable, Text> output, Reporter reporter) throws IOException {

            Map<String, Double> result = new HashMap<String, Double>();

            while (values.hasNext()) {

                String[] str = values.next().toString().split(",");

                if (result.containsKey(str[0])) {

                    result.put(str[0], result.get(str[0]) + Double.parseDouble(str[1]));

                } else {

                    result.put(str[0], Double.parseDouble(str[1]));

                }

            }

            Iterator iter = result.keySet().iterator();

            while (iter.hasNext()) {

                String itemID = iter.next();

                double score = result.get(itemID);

                v.set(itemID + "," + score);

                output.collect(key, v);

            }

        }

    }



    public static void run(Map<String, String> path) throws IOException {

        JobConf conf = Recommend.config();



        String input1 = path.get("Step4Input1");

        String input2 = path.get("Step4Input2");

        String output = path.get("Step4Output");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        conf.setOutputKeyClass(IntWritable.class);

        conf.setOutputValueClass(Text.class);



        conf.setMapperClass(Step4_PartialMultiplyMapper.class);

        conf.setCombinerClass(Step4_AggregateAndRecommendReducer.class);

        conf.setReducerClass(Step4_AggregateAndRecommendReducer.class);



        conf.setInputFormat(TextInputFormat.class);

        conf.setOutputFormat(TextOutputFormat.class);



        FileInputFormat.setInputPaths(conf, new Path(input1), new Path(input2));

        FileOutputFormat.setOutputPath(conf, new Path(output));



        RunningJob job = JobClient.runJob(conf);

        while (!job.isComplete()) {

            job.waitForCompletion();

        }

    }



}



class Cooccurrence {

    private int itemID1;

    private int itemID2;

    private int num;



    public Cooccurrence(int itemID1, int itemID2, int num) {

        super();

        this.itemID1 = itemID1;

        this.itemID2 = itemID2;

        this.num = num;

    }



    public int getItemID1() {

        return itemID1;

    }



    public void setItemID1(int itemID1) {

        this.itemID1 = itemID1;

    }



    public int getItemID2() {

        return itemID2;

    }



    public void setItemID2(int itemID2) {

        this.itemID2 = itemID2;

    }



    public int getNum() {

        return num;

    }



    public void setNum(int num) {

        this.num = num;

    }



}

计算结果：



~ hadoop fs -cat /user/hdfs/recommend/step4/part-00000



1       107,5.0

1       106,18.0

1       105,15.5

1       104,33.5

1       103,39.0

1       102,31.5

1       101,44.0

2       107,4.0

2       106,20.5

2       105,15.5

2       104,36.0

2       103,41.5

2       102,32.5

2       101,45.5

3       107,15.5

3       106,16.5

3       105,26.0

3       104,38.0

3       103,24.5

3       102,18.5

3       101,40.0

4       107,9.5

4       106,33.0

4       105,26.0

4       104,55.0

4       103,53.5

4       102,37.0

4       101,63.0

5       107,11.5

5       106,34.5

5       105,32.0

5       104,59.0

5       103,56.5

5       102,42.5

5       101,68.0

对Step4过程优化，请参考本文最后的补充内容。

6). HdfsDAO.java，HDFS操作工具类
详细解释，请参考文章：Hadoop编程调用HDFS

源代码：



package org.conan.myhadoop.hdfs;



import java.io.IOException;

import java.net.URI;



import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FSDataInputStream;

import org.apache.hadoop.fs.FSDataOutputStream;

import org.apache.hadoop.fs.FileStatus;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IOUtils;

import org.apache.hadoop.mapred.JobConf;



public class HdfsDAO {



    private static final String HDFS = "hdfs://192.168.1.210:9000/";



    public HdfsDAO(Configuration conf) {

        this(HDFS, conf);

    }



    public HdfsDAO(String hdfs, Configuration conf) {

        this.hdfsPath = hdfs;

        this.conf = conf;

    }



    private String hdfsPath;

    private Configuration conf;



    public static void main(String[] args) throws IOException {

        JobConf conf = config();

        HdfsDAO hdfs = new HdfsDAO(conf);

        hdfs.copyFile("datafile/item.csv", "/tmp/new");

        hdfs.ls("/tmp/new");

    }        



    public static JobConf config(){

        JobConf conf = new JobConf(HdfsDAO.class);

        conf.setJobName("HdfsDAO");

        conf.addResource("classpath:/hadoop/core-site.xml");

        conf.addResource("classpath:/hadoop/hdfs-site.xml");

        conf.addResource("classpath:/hadoop/mapred-site.xml");

        return conf;

    }



    public void mkdirs(String folder) throws IOException {

        Path path = new Path(folder);

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        if (!fs.exists(path)) {

            fs.mkdirs(path);

            System.out.println("Create: " + folder);

        }

        fs.close();

    }



    public void rmr(String folder) throws IOException {

        Path path = new Path(folder);

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        fs.deleteOnExit(path);

        System.out.println("Delete: " + folder);

        fs.close();

    }



    public void ls(String folder) throws IOException {

        Path path = new Path(folder);

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        FileStatus[] list = fs.listStatus(path);

        System.out.println("ls: " + folder);

        System.out.println("==========================================================");

        for (FileStatus f : list) {

            System.out.printf("name: %s, folder: %s, size: %d\n", f.getPath(), f.isDir(), f.getLen());

        }

        System.out.println("==========================================================");

        fs.close();

    }



    public void createFile(String file, String content) throws IOException {

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        byte[] buff = content.getBytes();

        FSDataOutputStream os = null;

        try {

            os = fs.create(new Path(file));

            os.write(buff, 0, buff.length);

            System.out.println("Create: " + file);

        } finally {

            if (os != null)

                os.close();

        }

        fs.close();

    }



    public void copyFile(String local, String remote) throws IOException {

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        fs.copyFromLocalFile(new Path(local), new Path(remote));

        System.out.println("copy from: " + local + " to " + remote);

        fs.close();

    }



    public void download(String remote, String local) throws IOException {

        Path path = new Path(remote);

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        fs.copyToLocalFile(path, new Path(local));

        System.out.println("download: from" + remote + " to " + local);

        fs.close();

    }



    public void cat(String remoteFile) throws IOException {

        Path path = new Path(remoteFile);

        FileSystem fs = FileSystem.get(URI.create(hdfsPath), conf);

        FSDataInputStream fsdis = null;

        System.out.println("cat: " + remoteFile);

        try {  

            fsdis =fs.open(path);

            IOUtils.copyBytes(fsdis, System.out, 4096, false);  

          } finally {  

            IOUtils.closeStream(fsdis);

            fs.close();

          }

    }

}

这样我们就自己编程实现了MapReduce化基于物品的协同过滤算法。

RHadoop的实现方案，请参考文章：RHadoop实践系列之三 R实现MapReduce的协同过滤算法

Mahout的实现方案，请参考文章：Mahout分步式程序开发 基于物品的协同过滤ItemCF

我已经把整个MapReduce的实现都放到了github上面：
https://github.com/bsspirit/maven_hadoop_template/releases/tag/recommend

6. 补充内容：对Step4过程优化

在Step4.java这一步运行过程中，Mapper过程在Step4_PartialMultiplyMapper类通过分别读取两个input数据，在内存中进行了计算。

这种方式有明显的限制条件：

  • a. 两个输入数据集，有严格的读入顺序。由于Hadoop不能指定读入顺序，因此在多节点的Hadoop集群环境，读入顺序有可能会发生错误，造成程序的空指针错误。
  • b. 这个计算过程，在内存中实现。如果矩阵过大，会造成单节点的内存不足。

做为优化的方案，我们需要对Step4的过程，实现MapReduce的矩阵乘法，矩阵算法原理请参考文章：用MapReduce实现矩阵乘法

对Step4优化的实现：把矩阵计算通过两个MapReduce过程实现。

  • 矩阵乘法过程类文件：Step4_Update.java
  • 矩阵加法过程类文件：Step4_Update2.java
  • 修改启动程序：Recommend.java

增加文件：Step4_Update.java



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.JobConf;

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.input.FileSplit;

import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step4_Update {



    public static class Step4_PartialMultiplyMapper extends Mapper {



        private String flag;// A同现矩阵 or B评分矩阵



        @Override

        protected void setup(Context context) throws IOException, InterruptedException {

            FileSplit split = (FileSplit) context.getInputSplit();

            flag = split.getPath().getParent().getName();// 判断读的数据集



            // System.out.println(flag);

        }



        @Override

        public void map(LongWritable key, Text values, Context context) throws IOException, InterruptedException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());



            if (flag.equals("step3_2")) {// 同现矩阵

                String[] v1 = tokens[0].split(":");

                String itemID1 = v1[0];

                String itemID2 = v1[1];

                String num = tokens[1];



                Text k = new Text(itemID1);

                Text v = new Text("A:" + itemID2 + "," + num);



                context.write(k, v);

                // System.out.println(k.toString() + "  " + v.toString());



            } else if (flag.equals("step3_1")) {// 评分矩阵

                String[] v2 = tokens[1].split(":");

                String itemID = tokens[0];

                String userID = v2[0];

                String pref = v2[1];



                Text k = new Text(itemID);

                Text v = new Text("B:" + userID + "," + pref);



                context.write(k, v);

                // System.out.println(k.toString() + "  " + v.toString());

            }

        }



    }



    public static class Step4_AggregateReducer extends Reducer {



        @Override

        public void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {

            System.out.println(key.toString() + ":");



            Map mapA = new HashMap();

            Map mapB = new HashMap();



            for (Text line : values) {

                String val = line.toString();

                System.out.println(val);



                if (val.startsWith("A:")) {

                    String[] kv = Recommend.DELIMITER.split(val.substring(2));

                    mapA.put(kv[0], kv[1]);



                } else if (val.startsWith("B:")) {

                    String[] kv = Recommend.DELIMITER.split(val.substring(2));

                    mapB.put(kv[0], kv[1]);



                }

            }



            double result = 0;

            Iterator iter = mapA.keySet().iterator();

            while (iter.hasNext()) {

                String mapk = iter.next();// itemID



                int num = Integer.parseInt(mapA.get(mapk));

                Iterator iterb = mapB.keySet().iterator();

                while (iterb.hasNext()) {

                    String mapkb = iterb.next();// userID

                    double pref = Double.parseDouble(mapB.get(mapkb));

                    result = num * pref;// 矩阵乘法相乘计算



                    Text k = new Text(mapkb);

                    Text v = new Text(mapk + "," + result);

                    context.write(k, v);

                    System.out.println(k.toString() + "  " + v.toString());

                }

            }

        }

    }



    public static void run(Map path) throws IOException, InterruptedException, ClassNotFoundException {

        JobConf conf = Recommend.config();



        String input1 = path.get("Step5Input1");

        String input2 = path.get("Step5Input2");

        String output = path.get("Step5Output");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        Job job = new Job(conf);

        job.setJarByClass(Step4_Update.class);



        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(Text.class);



        job.setMapperClass(Step4_Update.Step4_PartialMultiplyMapper.class);

        job.setReducerClass(Step4_Update.Step4_AggregateReducer.class);



        job.setInputFormatClass(TextInputFormat.class);

        job.setOutputFormatClass(TextOutputFormat.class);



        FileInputFormat.setInputPaths(job, new Path(input1), new Path(input2));

        FileOutputFormat.setOutputPath(job, new Path(output));



        job.waitForCompletion(true);

    }



}

增加文件：Step4_Update2.java



package org.conan.myhadoop.recommend;



import java.io.IOException;

import java.util.HashMap;

import java.util.Iterator;

import java.util.Map;



import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.LongWritable;

import org.apache.hadoop.io.Text;

import org.apache.hadoop.mapred.JobConf;

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.input.TextInputFormat;

import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Step4_Update2 {



    public static class Step4_RecommendMapper extends Mapper {



        @Override

        public void map(LongWritable key, Text values, Context context) throws IOException, InterruptedException {

            String[] tokens = Recommend.DELIMITER.split(values.toString());

            Text k = new Text(tokens[0]);

            Text v = new Text(tokens[1]+","+tokens[2]);

            context.write(k, v);

        }

    }



    public static class Step4_RecommendReducer extends Reducer {

        

        @Override

        public void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {

            System.out.println(key.toString() + ":");

            Map map = new HashMap();// 结果

            

            for (Text line : values) {

                System.out.println(line.toString());

                String[] tokens = Recommend.DELIMITER.split(line.toString());

                String itemID = tokens[0];

                Double score = Double.parseDouble(tokens[1]);

                

                 if (map.containsKey(itemID)) {

                     map.put(itemID, map.get(itemID) + score);// 矩阵乘法求和计算

                 } else {

                     map.put(itemID, score);

                 }

            }

            

            Iterator iter = map.keySet().iterator();

            while (iter.hasNext()) {

                String itemID = iter.next();

                double score = map.get(itemID);

                Text v = new Text(itemID + "," + score);

                context.write(key, v);

            }

        }

    }



    public static void run(Map path) throws IOException, InterruptedException, ClassNotFoundException {

        JobConf conf = Recommend.config();



        String input = path.get("Step6Input");

        String output = path.get("Step6Output");



        HdfsDAO hdfs = new HdfsDAO(Recommend.HDFS, conf);

        hdfs.rmr(output);



        Job job = new Job(conf);

        job.setJarByClass(Step4_Update2.class);



        job.setOutputKeyClass(Text.class);

        job.setOutputValueClass(Text.class);



        job.setMapperClass(Step4_Update2.Step4_RecommendMapper.class);

        job.setReducerClass(Step4_Update2.Step4_RecommendReducer.class);



        job.setInputFormatClass(TextInputFormat.class);

        job.setOutputFormatClass(TextOutputFormat.class);



        FileInputFormat.setInputPaths(job, new Path(input));

        FileOutputFormat.setOutputPath(job, new Path(output));



        job.waitForCompletion(true);

    }



}

修改Recommend.java



package org.conan.myhadoop.recommend;



import java.util.HashMap;

import java.util.Map;

import java.util.regex.Pattern;



import org.apache.hadoop.mapred.JobConf;

import org.conan.myhadoop.hdfs.HdfsDAO;



public class Recommend {



    public static final String HDFS = "hdfs://192.168.1.210:9000";

    public static final Pattern DELIMITER = Pattern.compile("[\t,]");



    public static void main(String[] args) throws Exception {

        Map path = new HashMap();

        path.put("data", "logfile/small.csv");

        path.put("Step1Input", HDFS + "/user/hdfs/recommend");

        path.put("Step1Output", path.get("Step1Input") + "/step1");

        path.put("Step2Input", path.get("Step1Output"));

        path.put("Step2Output", path.get("Step1Input") + "/step2");

        path.put("Step3Input1", path.get("Step1Output"));

        path.put("Step3Output1", path.get("Step1Input") + "/step3_1");

        path.put("Step3Input2", path.get("Step2Output"));

        path.put("Step3Output2", path.get("Step1Input") + "/step3_2");

        

        path.put("Step4Input1", path.get("Step3Output1"));

        path.put("Step4Input2", path.get("Step3Output2"));

        path.put("Step4Output", path.get("Step1Input") + "/step4");

        

        path.put("Step5Input1", path.get("Step3Output1"));

        path.put("Step5Input2", path.get("Step3Output2"));

        path.put("Step5Output", path.get("Step1Input") + "/step5");

        

        path.put("Step6Input", path.get("Step5Output"));

        path.put("Step6Output", path.get("Step1Input") + "/step6");       



        Step1.run(path);

        Step2.run(path);

        Step3.run1(path);

        Step3.run2(path);

        //Step4.run(path);

        

        Step4_Update.run(path);

        Step4_Update2.run(path);

               

        System.exit(0);

    }



    public static JobConf config() {

        JobConf conf = new JobConf(Recommend.class);

        conf.setJobName("Recommand");

        conf.addResource("classpath:/hadoop/core-site.xml");

        conf.addResource("classpath:/hadoop/hdfs-site.xml");

        conf.addResource("classpath:/hadoop/mapred-site.xml");

        conf.set("io.sort.mb", "1024");

        return conf;

    }



}

运行Step4_Update.java，查看输出结果



~ hadoop fs -cat /user/hdfs/recommend/step5/part-r-00000



3       107,2.0

2       107,2.0

1       107,5.0

5       107,4.0

4       107,5.0

3       106,4.0

2       106,4.0

1       106,10.0

5       106,8.0

4       106,10.0

3       105,4.0

2       105,4.0

1       105,10.0

5       105,8.0

4       105,10.0

3       104,8.0

2       104,8.0

1       104,20.0

5       104,16.0

4       104,20.0

3       103,8.0

2       103,8.0

1       103,20.0

5       103,16.0

4       103,20.0

3       102,6.0

2       102,6.0

1       102,15.0

5       102,12.0

4       102,15.0

3       101,10.0

2       101,10.0

1       101,25.0

5       101,20.0

4       101,25.0

2       106,2.5

1       106,3.0

5       106,3.0

2       105,2.5

1       105,3.0

5       105,3.0

2       104,5.0

1       104,6.0

5       104,6.0

2       103,7.5

1       103,9.0

5       103,9.0

2       102,7.5

1       102,9.0

5       102,9.0

2       101,7.5

1       101,9.0

5       101,9.0

2       106,10.0

1       106,5.0

5       106,4.0

4       106,6.0

2       105,5.0

1       105,2.5

5       105,2.0

4       105,3.0

2       104,15.0

1       104,7.5

5       104,6.0

4       104,9.0

2       103,20.0

1       103,10.0

5       103,8.0

4       103,12.0

2       102,15.0

1       102,7.5

5       102,6.0

4       102,9.0

2       101,20.0

1       101,10.0

5       101,8.0

4       101,12.0

3       107,4.0

2       107,2.0

5       107,4.0

4       107,4.5

3       106,8.0

2       106,4.0

5       106,8.0

4       106,9.0

3       105,8.0

2       105,4.0

5       105,8.0

4       105,9.0

3       104,16.0

2       104,8.0

5       104,16.0

4       104,18.0

3       103,12.0

2       103,6.0

5       103,12.0

4       103,13.5

3       102,8.0

2       102,4.0

5       102,8.0

4       102,9.0

3       101,16.0

2       101,8.0

5       101,16.0

4       101,18.0

3       107,4.5

5       107,3.5

3       106,4.5

5       106,3.5

3       105,9.0

5       105,7.0

3       104,9.0

5       104,7.0

3       103,4.5

5       103,3.5

3       102,4.5

5       102,3.5

3       101,9.0

5       101,7.0

5       106,8.0

4       106,8.0

5       105,4.0

4       105,4.0

5       104,8.0

4       104,8.0

5       103,8.0

4       103,8.0

5       102,4.0

4       102,4.0

5       101,8.0

4       101,8.0

3       107,5.0

3       105,5.0

3       104,5.0

3       101,5.0

运行Step4_Update2.java，查看输出结果



~ hadoop fs -cat /user/hdfs/recommend/step6/part-r-00000



1       107,5.0

1       106,18.0

1       105,15.5

1       104,33.5

1       103,39.0

1       102,31.5

1       101,44.0

2       107,4.0

2       106,20.5

2       105,15.5

2       104,36.0

2       103,41.5

2       102,32.5

2       101,45.5

3       107,15.5

3       106,16.5

3       105,26.0

3       104,38.0

3       103,24.5

3       102,18.5

3       101,40.0

4       107,9.5

4       106,33.0

4       105,26.0

4       104,55.0

4       103,53.5

4       102,37.0

4       101,63.0

5       107,11.5

5       106,34.5

5       105,32.0

5       104,59.0

5       103,56.5

5       102,42.5

5       101,68.0

这样我们就把原来内存中计算的部分，通过MapReduce实现了，结果与之间Step4的结果一致。

作者介绍：

张丹，R语言中文社区专栏特邀作者，《R的极客理想》系列图书作者，民生银行大数据中心数据分析师，前况客创始人兼CTO。

10年IT编程背景，精通R ,Java, Nodejs 编程，获得10项SUN及IBM技术认证。丰富的互联网应用开发架构经验，金融大数据专家。个人博客 http://fens.me， Alexa全球排名70k。

著有《R的极客理想-工具篇》、《R的极客理想-高级开发篇》，合著《数据实践之美》，新书《R的极客理想-量化投资篇》(即将出版)。

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