# recbole.evaluator.metrics¶

recbole.evaluator.metrics.auc_(trues, preds)[source]

AUC (also known as Area Under Curve) is used to evaluate the two-class model, referring to the area under the ROC curve

Note

This metric does not calculate group-based AUC which considers the AUC scores averaged across users. It is also not limited to k. Instead, it calculates the scores on the entire prediction results regardless the users.

$\mathrm {AUC} = \frac{\sum\limits_{i=1}^M rank_{i} - \frac {{M} \times {(M+1)}}{2}} {{{M} \times {N}}}$

$$M$$ is the number of positive samples. $$N$$ is the number of negative samples. $$rank_i$$ is the ascending rank of the ith positive sample.

recbole.evaluator.metrics.gauc_(user_len_list, pos_len_list, pos_rank_sum)[source]

GAUC (also known as Group Area Under Curve) is used to evaluate the two-class model, referring to the area under the ROC curve grouped by user.

Note

It calculates the AUC score of each user, and finally obtains GAUC by weighting the user AUC. It is also not limited to k. Due to our padding for scores_tensor in RankEvaluator with -np.inf, the padding value will influence the ranks of origin items. Therefore, we use descending sort here and make an identity transformation to the formula of AUC, which is shown in auc_ function. For readability, we didn’t do simplification in the code.

$\mathrm {GAUC} = \frac {{{M} \times {(M+N+1)} - \frac{M \times (M+1)}{2}} - \sum\limits_{i=1}^M rank_{i}} {{M} \times {N}}$

$$M$$ is the number of positive samples. $$N$$ is the number of negative samples. $$rank_i$$ is the descending rank of the ith positive sample.

recbole.evaluator.metrics.hit_(pos_index, pos_len)[source]

Hit (also known as hit ratio at $$N$$) is a way of calculating how many ‘hits’ you have in an n-sized list of ranked items.

$\mathrm {HR@K} =\frac{Number \space of \space Hits @K}{|GT|}$

$$HR$$ is the number of users with a positive sample in the recommendation list. $$GT$$ is the total number of samples in the test set.

recbole.evaluator.metrics.log_loss_(trues, preds)[source]

Log loss, aka logistic loss or cross-entropy loss

$-\log {P(y_t|y_p)} = -(({y_t}\ \log{y_p}) + {(1-y_t)}\ \log{(1 - y_p)})$

For a single sample, $$y_t$$ is true label in $$\{0,1\}$$. $$y_p$$ is the estimated probability that $$y_t = 1$$.

recbole.evaluator.metrics.mae_(trues, preds)[source]

Mean absolute error regression loss

$\mathrm{MAE}=\frac{1}{|{T}|} \sum_{(u, i) \in {T}}\left|\hat{r}_{u i}-r_{u i}\right|$

$$T$$ is the test set, $$\hat{r}_{u i}$$ is the score predicted by the model, and $$r_{u i}$$ the actual score of the test set.

recbole.evaluator.metrics.map_(pos_index, pos_len)[source]

MAP (also known as Mean Average Precision) The MAP is meant to calculate Avg. Precision for the relevant items.

Note

In this case the normalization factor used is $$\frac{1}{\min (m,N)}$$, which prevents your AP score from being unfairly suppressed when your number of recommendations couldn’t possibly capture all the correct ones.

\begin{split}\begin{align*} \mathrm{AP@N} &= \frac{1}{\mathrm{min}(m,N)}\sum_{k=1}^N P(k) \cdot rel(k) \\ \mathrm{MAP@N}& = \frac{1}{|U|}\sum_{u=1}^{|U|}(\mathrm{AP@N})_u \end{align*}\end{split}
recbole.evaluator.metrics.mrr_(pos_index, pos_len)[source]

The MRR (also known as mean reciprocal rank) is a statistic measure for evaluating any process that produces a list of possible responses to a sample of queries, ordered by probability of correctness.

$\mathrm {MRR} = \frac{1}{|{U}|} \sum_{i=1}^{|{U}|} \frac{1}{rank_i}$

$$U$$ is the number of users, $$rank_i$$ is the rank of the first item in the recommendation list in the test set results for user $$i$$.

recbole.evaluator.metrics.ndcg_(pos_index, pos_len)[source]

NDCG (also known as normalized discounted cumulative gain) is a measure of ranking quality. Through normalizing the score, users and their recommendation list results in the whole test set can be evaluated.

$\begin{split}\begin{gather} \mathrm {DCG@K}=\sum_{i=1}^{K} \frac{2^{rel_i}-1}{\log_{2}{(i+1)}}\\ \mathrm {IDCG@K}=\sum_{i=1}^{K}\frac{1}{\log_{2}{(i+1)}}\\ \mathrm {NDCG_u@K}=\frac{DCG_u@K}{IDCG_u@K}\\ \mathrm {NDCG@K}=\frac{\sum \nolimits_{u \in U^{te}NDCG_u@K}}{|U^{te}|} \end{gather}\end{split}$

$$K$$ stands for recommending $$K$$ items. And the $$rel_i$$ is the relevance of the item in position $$i$$ in the recommendation list. $${rel_i}$$ equals to 1 if the item is ground truth otherwise 0. $$U^{te}$$ stands for all users in the test set.

recbole.evaluator.metrics.precision_(pos_index, pos_len)[source]

Precision (also called positive predictive value) is the fraction of relevant instances among the retrieved instances

$\mathrm {Precision@K} = \frac{|Rel_u \cap Rec_u|}{Rec_u}$

$$Rel_u$$ is the set of items relevant to user $$U$$, $$Rec_u$$ is the top K items recommended to users. We obtain the result by calculating the average $$Precision@K$$ of each user.

recbole.evaluator.metrics.recall_(pos_index, pos_len)[source]

Recall (also known as sensitivity) is the fraction of the total amount of relevant instances that were actually retrieved

$\mathrm {Recall@K} = \frac{|Rel_u\cap Rec_u|}{Rel_u}$

$$Rel_u$$ is the set of items relevant to user $$U$$, $$Rec_u$$ is the top K items recommended to users. We obtain the result by calculating the average $$Recall@K$$ of each user.

recbole.evaluator.metrics.rmse_(trues, preds)[source]

Mean std error regression loss

$\mathrm{RMSE} = \sqrt{\frac{1}{|{T}|} \sum_{(u, i) \in {T}}(\hat{r}_{u i}-r_{u i})^{2}}$

$$T$$ is the test set, $$\hat{r}_{u i}$$ is the score predicted by the model, and $$r_{u i}$$ the actual score of the test set.