Bug in preprocess_in_batches

[avantikalal]

In the preprocess_in_batches function, we filter genes first, before filtering / subsetting cells. https://github.com/clara-parabricks/rapids-single-cell-examples/blob/master/notebooks/rapids_scanpy_funcs.py#L779

This leads to two (minor) discrepancies -

• first, it is different from the CPU version of filtering, where we filter cells first and genes second.
• Second, if we are selecting a subset of cells (e.g. 50K, 250K) from the 1M cell dataset, the genes will be filtered based on their occurrence in the whole dataset, instead of only in the subset of selected cells.