How to split a list based on tuple content in Python

I have a list of 3-tuples, and I want to split them on the last coordinate. So for example if the input were:

[(1,2,x), (2,3,x), (1,2,z), (2,20,z)]

I’d want the output to be

[(1,2,x),(2,3,x)],[(1,2,z),(2,20,z)]

My current approach involves getting all N distinct 3rd indices and looping over the list N times to build the list of lists. I am wondering if there is a pythonic way to do this without looping multiple times.

>Solution :

here is one way with complexity of O(n):

lt = [(1,2,'x'), (2,3,'x'), (1,2,'z'), (2,20,'z')]

res = {}
for i in lt:
  res.setdefault(i[2], []).append(i)

print(list(res.values()))

output:

>>>
[[(1, 2, 'x'), (2, 3, 'x')], [(1, 2, 'z'), (2, 20, 'z')]]