of classes the this is something that optimization based approaches can handle very gracefully because you can simply compete your loss function over different batches of data points very very naturally blackbox approaches you can do it but you need to train it for to be able to do that you need to be able to train it with variable data set sizes and variable numbers of examples per class and nonparametric approaches can also handle it fairly gracefully but in practice we found them not to always work well to to variable numbers of data