From what I understand from previously answered questions, you're meant to do your pre-processing on each set after splitting your data into training and test sets. But I'm not sure where the validation set comes into this. Do I also pre-process it separately to the training set? Or do I pre-process the training set as a whole and then separate the validation set?
I'm 99% sure you're meant to do all three of them separately, but the way my assignment is worded put me in some doubt so I thought I'd seek an answer/opinion here.