How to split strings within a list into separate strings

Question

This is a list I have.

x = [['E,4'], ['F,1']]

How to I split the individual subsections of the list into something else that looks like:

x = [['E'], [4], ['F'], [1]]

Answer 1

In [23]: x = [['E,4'], ['F,1']]

In [24]: [[e] for sub in x for s in sub for e in s.split(',')]
Out[24]: [['E'], ['4'], ['F'], ['1']]

Answer 2

It looks like the kind of question that might be easier to answer with more context. But still, how about:

L = [['E,4'], ['F,1']]

output = []
for pair in L:
    x, y = pair[0].split(',')
    output.append([x])
    output.append([int(y)])

>>>output
[['E'], [4], ['F'], [1]]