Mahout实现基于用户的协同过滤算法

Mahout中对协同过滤算法进行了封装，看一个简单的基于用户的协同过滤算法。

基于用户：通过用户对物品的偏好程度来计算出用户的在喜好上的近邻，从而根据近邻的喜好推测出用户的喜好并推荐。

图片来源

程序中用到的数据都存在MySQL数据库中，计算结果也存在MySQL中的对应用户表中。

package com.mahout.helloworlddemo;

import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.HashSet;
import java.util.List;

import org.apache.mahout.cf.taste.impl.model.jdbc.MySQLJDBCDataModel;
import org.apache.mahout.cf.taste.impl.neighborhood.NearestNUserNeighborhood;
import org.apache.mahout.cf.taste.impl.recommender.GenericUserBasedRecommender;
import org.apache.mahout.cf.taste.impl.similarity.PearsonCorrelationSimilarity;
import org.apache.mahout.cf.taste.model.DataModel;
import org.apache.mahout.cf.taste.model.JDBCDataModel;
import org.apache.mahout.cf.taste.neighborhood.UserNeighborhood;
import org.apache.mahout.cf.taste.recommender.RecommendedItem;
import org.apache.mahout.cf.taste.recommender.Recommender;
import org.apache.mahout.cf.taste.similarity.UserSimilarity;

import com.mahout.util.DBUtil;
import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;

/**
 *
 *@author wxisme
 *@time 2015-9-13 下午6:25:26
 */
public class RecommenderIntroFromMySQL {

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

        //连接MySQL
        MysqlDataSource dataSource = new MysqlDataSource();
        dataSource.setServerName("localhost");
        dataSource.setUser("root");
        dataSource.setPassword("1234");
        dataSource.setDatabaseName("mahoutdemo");

        //获取数据模型
        JDBCDataModel dataModel = new MySQLJDBCDataModel(dataSource, "taste_preferences", "user_id", "item_id", "preference","time");

        DataModel model = dataModel;

        //计算相似度
        UserSimilarity similarity = new PearsonCorrelationSimilarity(model);
        //计算阈值
        UserNeighborhood neighborhood = new NearestNUserNeighborhood(2,similarity,model);

        //推荐
        Recommender recommender = new GenericUserBasedRecommender(model,neighborhood,similarity);

        Connection con = DBUtil.getConnection();
        Statement stmt = con.createStatement();

        //获取每个用户的推荐数据并存入数据库

        for(int i=0; i<5; i++) {
            List<RecommendedItem> recommendations = recommender.recommend(i, 3);

            String tableName = "user_" + i;

            for (RecommendedItem recommendation : recommendations) {

                //如果是第一次推荐就创建该用户的数据表
                if(!doesTableExist(tableName)) {

                    String createSQL = "create table " + tableName
                            + " (item_id bigint primary key,value float);";
                    stmt.execute(createSQL);
                }

                String insertSQL = "insert into " + tableName + " values ("
                        + recommendation.getItemID() + "," + recommendation.getValue() + " );";

                //插入用户的推荐数据
                stmt.execute(insertSQL);

                System.out.println(recommendation);
            }
        }

    }

    /**
     * 是否存在这个数据表
     * @param tablename
     * @return
     * @throws SQLException
     */
    public static Boolean doesTableExist(String tablename) throws SQLException {
        HashSet<String> set = new HashSet<String>();
        Connection con = DBUtil.getConnection();
        DatabaseMetaData meta = con.getMetaData();
        ResultSet res = meta.getTables(null, null, null,
                new String[]{"TABLE"});
        while (res.next()) {
            set.add(res.getString("TABLE_NAME"));
        }
        DBUtil.close(res, con);
        return set.contains(tablename);
    }

}

测试数据：

1,101,5
1,102,3
1,103,2.5
2,101,2
2,102,2.5
2,103,5
2,104,2
3,101,2.5
3,104,4
3,105,4.5
3,107,5
4,101,5
4,103,3
4,104,4.5
4,106,4
5,101,4
5,102,3
5,103,2
5,104,4
5,105,3.5
5,106,4

运行结果：

更多Mahout和协同过滤算法的介绍与分析：

http://www.cnblogs.com/dlts26/archive/2011/08/23/2150225.html

http://www.tuicool.com/articles/FzmQziz

http://www.ibm.com/developerworks/cn/web/1103_zhaoct_recommstudy2/