我的推荐人推荐空列表

Question

请查看以下代码。我正在使用movielens 100k数据集。但是推荐者没有返回推荐项目列表，它返回一个空列表。我哪里出错了？

package org.psneog;
import java.io.File;
import java.io.IOException;
import java.util.List;
import org.apache.mahout.cf.taste.common.TasteException;
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.RecommendedItem;
import org.apache.mahout.cf.taste.recommender.Recommender;
import org.apache.mahout.cf.taste.similarity.UserSimilarity;


public class MyUserBasedRecommender {
    public void myrecommend(String filename) throws IOException, TasteException {   
       System.out.println("BEGIN myrecommend");
        DataModel model = new FileDataModel(new File(filename));
        System.out.println("MARK1 " + model.getNumItems());
        UserSimilarity similarity = new PearsonCorrelationSimilarity(model);
        System.out.println("MARK2 " + similarity);
        UserNeighborhood neighborhood = new NearestNUserNeighborhood(2, similarity, model);
        System.out.println("MARK3 " + neighborhood);
        Recommender recommender = new GenericUserBasedRecommender(model, neighborhood, similarity);
        System.out.println("MARK4 " + recommender);
        List<RecommendedItem> recommendations = recommender.recommend(751, 10);
        System.out.println("MARK5 "+ recommendations );
        for(RecommendedItem recommendation: recommendations){
            System.out.println(recommendation);
            System.out.println("MARK6");
        }
        System.out.println("END myrecommend");
    }

    public static void main(String[] args) throws IOException, TasteException {
        System.out.println("BEGIN");
        MyUserBasedRecommender myreco = new MyUserBasedRecommender();
        myreco.myrecommend("ml-100k/u.csv");
        System.out.println("END");
    }
}

它在MARK5显示一个空列表：

BEGIN
BEGIN myrecommend
MARK1 997
MARK2 PearsonCorrelationSimilarity[dataModel:FileDataModel[dataFile:C:\Users\Prabhakar\workspace_reco\MahoutEvaluation\ml-100k\u.csv],inferrer:null]
MARK3 NearestNUserNeighborhood
MARK4 GenericUserBasedRecommender[neighborhood:NearestNUserNeighborhood]
MARK5 []
END myrecommend
END

请帮帮我