veingrow veingrow - 4 months ago 33
Python Question

Count sub_lists length in python3

My python is 3 ver.
I have a list, which contains sub lists, like:

L=[[1,2], [3,4], [5,6,7]]

I want to calculate length of all sub_list and write down them to a dictionary, like this:


that is, we have 2 lists which have length 2, and 1 list which have the length 3.

It can be done by for-loop + check D[key] is exist or not.

May be there is some 'pythonic way?'


Use defaultdict where you store the length of the list as the key, and just increment each value by 1 every time to get a matching list length:

from collections import defaultdict

d = defaultdict(int)
L = [[1,2], [3,4], [5,6,7]]

for li in L:
    d[len(li)] += 1

print(d) # defaultdict(<class 'int'>, {2: 2, 3: 1})

Or use Counter from collections as well:

from collections import Counter

c = Counter(len(li) for li in L)

print(c) # Counter({2: 2, 3: 1})