What is the proper order of normalization steps before and after splitting data
Assuming I understand it correctly, I think your process is ok this way but I'm not sure about step 3 &quot;standardization&quot;:

Steps 1 and 2 are ok since this cannot leak any kind of information from the test set to the training set.
If the standardization step involves calculating values (e.g. mean and s.d.) over the whole data (including test set) and then standardizing the whole data using these values, then that could be an issue. I'd suggest moving step 3 after the split, so that standardization is based only on the training set and then applied &quot;as is&quot; to the test set.