What are the correct edge case values of precision and recall and how to integrate them into cross validation?

Question

I'm doing 10-fold cross validation on a dataset. But in some folds there are edge cases that the denominator in precision-recall calculation is zero (tp + fp =0).

What are the correct values for precision and recall in this case? And what is the correct way of doing cross-validation (should I include these results when reporting average precision-recall over 10 folds)?

PS: This question is very similar to What are correct values for precision and recall when the denominators equal 0?

Thanks in advance : -)

Answer 1

Instead of using CV to estimate precision and recall, use it to obtain the expected TP, TN, FP, and FN rate. Then use those values to compute the expected precision and recall and the standard errors. (Taylor expansions come in handy for the latter.)