Package es.upm.etsisi.cf4j.qualityMeasure.recommendation

Class NDCG

java.lang.Object

es.upm.etsisi.cf4j.qualityMeasure.QualityMeasure

es.upm.etsisi.cf4j.qualityMeasure.recommendation.NDCG

public class NDCG
extends QualityMeasure

This class calculates the Normalized Discounted Cumulative Gain (nDCG) of the recommendations performed by a Recommender. It is calculated as follows:

NDCG = <DCG> / <IDCG>

Field Summary

Fields inherited from class es.upm.etsisi.cf4j.qualityMeasure.QualityMeasure

recommender

Constructor Summary

Constructors

Constructor	Description
NDCG(Recommender recommender, int numberOfRecommendations)	Constructor
NDCG(Recommender recommender, Map<String,Object> params)	Constructor from a Map object with the quality measure parameters.

Method Summary

Modifier and Type	Method	Description
protected double	dataCalculation(TestUser testUser, int[] elements)	Function to process de data in the NDCG algorithm.
protected double	getScore(TestUser testUser, double[] predictions)	Computes the quality measure score for a TestUser given the predictions for his/her test ratings

Methods inherited from class es.upm.etsisi.cf4j.qualityMeasure.QualityMeasure

getScore, getScore

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

NDCG

public NDCG(Recommender recommender,
            Map<String,Object> params)

Constructor from a Map object with the quality measure parameters. Map object must contains the following keys:

• numberOfRecommendations: int value with the number of items to be recommended.

Parameters:

recommender - Recommender instance for which the NDCG are going to be computed

params - Quality measure's parameters

NDCG

public NDCG(Recommender recommender,
            int numberOfRecommendations)

Constructor

Parameters:

recommender - Recommender instance for which the nDCG are going to be computed

numberOfRecommendations - Number of recommendations

Method Detail

getScore

protected double getScore(TestUser testUser,
                          double[] predictions)

Description copied from class: QualityMeasure

Computes the quality measure score for a TestUser given the predictions for his/her test ratings

Specified by:

getScore in class QualityMeasure

Parameters:

testUser - TestUser for which the quality measure score is computed

predictions - Prediction value for the test items rated by the test user

Returns:

Quality measure score

dataCalculation

protected double dataCalculation(TestUser testUser,
                                 int[] elements)

Function to process de data in the NDCG algorithm. Extracted in order to dont repeat code.

Parameters:

testUser - Related used

elements - Recomendations or ideal recommendations

Returns:

discounted cumulative gain