I'm trying to understand precision and recall with an intuitive example, but my calculation doesn't seem right.
For example, there are 8 red balls and 2 blue ones. I'm stupid and just predict all of them are red. The accuracy would be 0.8 and looks good. But it doesn't reflect that it's just a lucky, stupid guess, and I missclassify all of the blue balls. If I'm not mistaken, we have 8 true positives (TP = 8), 2 false positives (FP = 2), and neither true nor false negatives (TN = 0, FN = 0) in this case. Then isn't precision = TP/(TP+FP) = 0.8 and recall = TP/(TP+FN) = 1? Don't they still look good?