I am evaluating a multi class classifier. As precision and recall are only defined for binary classification I want to create precision recall curves for every class by separating one class from all other classes. Using one-vs-all SVMs it’s very simple. For each class the appropriate SVM delivers a score which can be used with multiple Thresholds to create the precision recall curve. But how does it work with the nearest neighbor classifier? Is it possible to create a meaningful precision recall curve for the NN classifier? How can I use the distance values to create a score which can be combined with several thresholds?