如何对包含冻结集的列表进行排序（python）

Question

I have a list of frozensets that I'd like to sort, Each of the frozensets contains a single integer value that results from an intersection operation between two sets:

k = frozenset(w) & frozenset(string.digits)
d[k] = w # w is the value
list(d) # sorted(d) doesn't work since the keys are sets and sets are unordered.

Here is the printed list:

[frozenset({'2'}), frozenset({'1'}), frozenset({'4'}), frozenset({'3'})]

How can I sort the list using the values contained in the sets?

Answer 1

You need to provide function as key to sorted which would accept frozenset as argument and return something which might be compared. If each frozenset has exactly 1 element and said element is always single digit then you might use max function (it will extract that single element, as sole element is always biggest element of frozenset ) that is

d1 = [frozenset({'2'}), frozenset({'1'}), frozenset({'4'}), frozenset({'3'})]
d2 = sorted(d1,key=max)
print(d2)

output

[frozenset({'1'}), frozenset({'2'}), frozenset({'3'}), frozenset({'4'})]

If you want to know more read Sorting HOW TO

Answer 2

Honestly, unless you really need to keep the elements as frozenset , the best might be to generate a list of values upstream ( [2, 1, 4, 3] ).

Anyway, to be able to sort the frozensets you need to make them ordered elements, for instance by converting to tuple . You can do this transparently using the key parameter of sorted or natsorted for strings :

from natsort import natsorted
l = [frozenset({'2'}), frozenset({'1'}), frozenset({'4'}), frozenset({'3'})]

natsorted(l, key=tuple)

output:

[frozenset({'1'}), frozenset({'2'}), frozenset({'3'}), frozenset({'4'})]

Answer 3

Previous answers can not sorted correctly, Because of strings

d = [frozenset({'224'}), frozenset({'346'}), frozenset({'2'}), frozenset({'22345'})]
sorted(d, key=lambda x: int(list(x)[0]))

Output:

[frozenset({'2'}),
 frozenset({'224'}),
 frozenset({'346'}),
 frozenset({'22345'})]