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[Python-ideas] Multiple level sorting in python where the order of some levels may or may not be reversed

Chris Angelico rosuav at gmail.com
Sun Oct 16 00:46:25 EDT 2016 
On Sun, Oct 16, 2016 at 3:29 PM, Alireza Rafiei
<alireza.rafiei94 at gmail.com> wrote:
> What I ended up doing is:
>
>> count_list = sorted(count_list,
>>                     key=lambda x: (x[1], map(lambda x: -x, map(ord,
>> x[0]))),
>>                     reverse=True)
>
>
> which works. Now my solution is very specific to structures like [(str,
> int)] where all strs are lower case and besides ord makes it to be both
> limited in use and also more difficult to add extra levels of sorting.

Interesting. Personally, I would invert this; if you're sorting by an
integer and a string, negate the integer, and keep the string as-is.
If that doesn't work, a custom class might help.

# untested
class Record:
    reverse = False, True, True, False, True
    def __init__(data):
        self.data = data
    def __lt__(self, other):
        for v1, v2, rev in zip(self.data, other.data, self.reverse):
            if v1 < v2: return rev
            if v2 > v1: return not rev
        return False

This is broadly similar to how tuple.__lt__ works, allowing you to
flip the logic of whichever ones you like.

ChrisA
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