mahout推荐4-评估GroupLens数据集

使用GroupLens数据集ua.base

这是一个tab分割的文件，用户Id，物品Id，评分（偏好值），以及附加信息。可用吗？之前使用的是CSV格式，现在是tsv格式，可用，使用FileDataModel

对mahout推荐2中的评估程序使用这个数据集测试：

package mahout;

import java.io.File;
import org.apache.mahout.cf.taste.common.TasteException;
import org.apache.mahout.cf.taste.eval.RecommenderBuilder;
import org.apache.mahout.cf.taste.eval.RecommenderEvaluator;
import org.apache.mahout.cf.taste.impl.eval.AverageAbsoluteDifferenceRecommenderEvaluator;
import org.apache.mahout.cf.taste.impl.model.file.FileDataModel;
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.neighborhood.UserNeighborhood;
import org.apache.mahout.cf.taste.recommender.Recommender;
import org.apache.mahout.cf.taste.similarity.UserSimilarity;
import org.apache.mahout.common.RandomUtils;

public class TestRecommenderEvaluator {

	public static void main(String[] args) throws Exception {
		//强制每次生成相同的随机值，生成可重复的结果
		RandomUtils.useTestSeed();
		//数据装填
		//DataModel model = new FileDataModel(new File("data/intro.csv"));
		DataModel model = new FileDataModel(new File("data/ua.base"));
		//推荐评估，使用平均值
		RecommenderEvaluator evaluator = new AverageAbsoluteDifferenceRecommenderEvaluator();
		//推荐评估，使用均方差
		//RecommenderEvaluator evaluator = new RMSRecommenderEvaluator();
		//用于生成推荐引擎的构建器，与上一例子实现相同
		RecommenderBuilder builder = new RecommenderBuilder() {
			
			public Recommender buildRecommender(DataModel model) throws TasteException {
				// TODO Auto-generated method stub
				//用户相似度，多种方法
				UserSimilarity similarity = new PearsonCorrelationSimilarity(model);
				//用户邻居
				UserNeighborhood neighborhood = new NearestNUserNeighborhood(2, similarity, model);
				//一个推荐器
				return new GenericUserBasedRecommender(model, neighborhood, similarity);
			}
		};
		//推荐程序评估值（平均差值）训练90%的数据，测试数据10%，《mahout in Action》使用的是0.7,但是出现结果为NaN
		double score = evaluator.evaluate(builder, null, model, 0.9, 1.0);
		System.out.println(score);
	}
}

 结果输出：

14/08/04 09:52:38 INFO file.FileDataModel: Creating FileDataModel for file data\ua.base
14/08/04 09:52:38 INFO file.FileDataModel: Reading file info...
14/08/04 09:52:38 INFO file.FileDataModel: Read lines: 90570
14/08/04 09:52:38 INFO model.GenericDataModel: Processed 943 users
14/08/04 09:52:38 INFO eval.AbstractDifferenceRecommenderEvaluator: Beginning evaluation using 0.9 of FileDataModel[dataFile:D:\workspace\zoodemo\data\ua.base]
14/08/04 09:52:38 INFO model.GenericDataModel: Processed 943 users
14/08/04 09:52:38 INFO eval.AbstractDifferenceRecommenderEvaluator: Beginning evaluation of 878 users
14/08/04 09:52:38 INFO eval.AbstractDifferenceRecommenderEvaluator: Starting timing of 878 tasks in 4 threads
14/08/04 09:52:39 INFO eval.StatsCallable: Average time per recommendation: 39ms
14/08/04 09:52:39 INFO eval.StatsCallable: Approximate memory used: 16MB / 79MB
14/08/04 09:52:39 INFO eval.StatsCallable: Unable to recommend in 114 cases
14/08/04 09:52:43 INFO eval.AbstractDifferenceRecommenderEvaluator: Evaluation result: 0.9375000000000002
0.9375000000000002

 现在是基于100 000 个偏好值，而不是少数几个

结果大约为0.9 在1到5的区间内，这个值偏离了将近一个点，不算太好。

也许我们正在使用的这个特定Recommender实现并不是最优的。