I am wondering what is the right way to use a sampler like WeightedRandomSampler for imbalanced classification problems.
Specifically, I am unclear as to whether I only use sampling during:

Training
Training + Validation
Training + Validation + Testing (whereby each gets its own sampler to capture the distribution in its respective data set)

I’ve poked through several threads and noticed people using it for training only and training + validation.
Thanks for your time and help!