eval_nDCG {rrecsys}

Normalized Discounted Cumulative Gain

Description

Metric for information retrival where positions are discounted logarithmically.

Usage

eval_nDCG(recommendedIDX, testSetIDX)

Arguments

recommendedIDX

indices of the recommended items. Object of class numeric.

testSetIDX

indices of the items in the test set. Object of class numeric

Details

nDCG is computed as the ratio between Discounted Cumulative Gain(DCG) and idealized Discounted Cumulative Gain(IDCG):

DGC_{pos} = rel_1 + \sum_{i=2}^{pos} \frac{rel_i}{\log_2i}

IDGC_{pos} = rel_1 + \sum_{i=2}^{|h|-1} \frac{rel_i}{\log_2i}

nDCG_{pos} = \frac{DCG}{IDCG}

References

Asela Gunawardana, Guy Shani, Evaluating Recommender Systems.