Python Beginner - How to generate a list and frequency from another list

Question

Given:

[['x','a'], ['y','b'], ['z','a']]

I would like a list of the elements and a count frequency of the 2nd element:

[['x','a',2], ['y','b',1], ['z','a',2]]

Answer 1

>>> from collections import Counter
>>> L = [['x','a'], ['y','b'], ['z','a']]
>>> freq = Counter(y for x, y in L)
>>> [[x, y, freq[y]] for x, y in L]
[['x', 'a', 2], ['y', 'b', 1], ['z', 'a', 2]]