We have a list of nested lists (list of matrices) that we wish to transpose.
Utilize chain to iterate over our master list (x), flattening it, and then we iterate over the elements and return these as a transposed list element.
We can also check that an iterated element exists and meets some value requirement (here, less than 200).
from itertools import chain [[y[i] for y in list(chain.from_iterable(x)) if y[i] and y[i] < 200] for i in range(0,len(x))]
Here, we are assuming that the subunits are invariable in length.