According to the formula of R-squared below (wiki), since I have only one predicted target value for each of the N folds, R2 is zero unless the predicted value coincides exactly with the true target value. This seems to render the application of R2
useless in this case. Are there other metrics I may use with a similar straightforward interpretation? What other ways exist to approach this problem?
P.S.: One alternative I came up with is computing R2 using the set of all predicted target values (from all N folds) and the true target values. However, this leaves me without an estimation of its variance. Has it a paper to support this approach?
same problem with (https://stats.stackexchange.com/questions/405872/leave-one-out-cross-validation-in-regression-r-squared-cannot-be-used-how-els?rq=1)