比较列表中的列表并计算出现次数

Question

If I have a list of lists a , I want a function f()

a = [[1,2,3],[1,2,3],[0,5,6],[0,5,4]]

that gives the output:

out = f(a)
out
>> {[1,2,3]:2,[0,5,6]:1,[0,5,4]:1]}

The order matters too, I need it to be completely similar I was going to use Counter but it does not work with lists. Sets are also out of the question. Is there some sort of 'easier' method than doing the whole thing from scratch maybe using something like Counter ?

Answer 1

Since dictionary keys can't have mutable objects, you would need to convert them to a tuple (a immutable object), then do Counter :

from collections import Counter
a = [[1,2,3],[1,2,3],[0,5,6],[0,5,4]]
print(Counter(map(tuple, a)))

Which outputs:

Counter({(1, 2, 3): 2, (0, 5, 6): 1, (0, 5, 4): 1})