Group list by values

Question

Let\'s say I have a list like this:

mylist = [["A",0], ["B",1], ["C",0], ["D",2], ["E",2]]

Answer 1

>>> import collections
>>> D1 = collections.defaultdict(list)
>>> for element in L1:
...     D1[element[1]].append(element[0])
... 
>>> L2 = D1.values()
>>> print L2
[['A', 'C'], ['B'], ['D', 'E']]
>>>