Reversing and then using the stable sort sounds like an elegant solution.
Thanks!
@Robert
I totally missed the indexes could refer to swapped items. I somehow had
the impression that go would memorize the returned order and swap them in
one go. This explains it. Thanks a lot.
On Wednesday, December 7, 2022 at 12:07:48 PM UTC+8 harr...@spu.edu wrote:
> > In my real code I have other criteria to compare the slice items, but if
> they tie, I want to use the reverse of their original order.
>
> Oh, forgot to say: FWIW - I think reversing and then sort.SliceStable
> might be a solution - asymptotically reverse should be less complex than
> the sort, or probably there are other variations that don't require
> reimplementing sorting.
> On Tuesday, December 6, 2022 at 7:47:04 PM UTC-8 Andrew Harris wrote:
>
>> Just as an intuitive argument, we could do:
>> sort.Slice(s, func(i, j int) bool { log.Println(i, j); return i > j })
>>
>> The appearances of i and j per step recapitulate the logic of the sorting
>> algo in some weak sense; not slice order
>> On Tuesday, December 6, 2022 at 7:28:39 PM UTC-8 hey...@gmail.com wrote:
>>
>>> > sorts defined by an ordering function purely dependent on the value of
>>> the element
>>>
>>> Hmm, I thought the function was agnostic to what really get compared? If
>>> it offers two index numbers, and the return value says the one with larger
>>> index number should be at the front, shouldn't the sort function simply do
>>> that, since during the sorting, the passed index number should be stable?
>>> On Wednesday, December 7, 2022 at 11:14:37 AM UTC+8 harr...@spu.edu
>>> wrote:
>>>
>>>> Oh, to reverse by index ... I think this doesn't quite fit in the idea
>>>> of sorts defined by an ordering function purely dependent on the value of
>>>> the element.
>>>>
>>>> I think there may have been a feature request
>>>> <https://github.com/golang/go/issues/47988> for a `slices.Reverse`
>>>> function in golang.org/x/exp/slices - I'm not sure what the status or
>>>> reasoning is on this. FWIW it's not the only approach that might make
>>>> sense
>>>> for traversing a slice in reverse order, and it can be naive when working
>>>> with e.g. bytes holding utf8.
>>>>
>>>> I think this works but I haven't really thought about edge cases...
>>>>
>>>> `reverse(&s)`
>>>>
>>>> func reverse[T any](s *[]T) {
>>>> z := len(*s)
>>>> for a := 0; a < len(*s)/2; a++ {
>>>> (*s)[a], (*s)[z-a-1] = (*s)[z-a-1], (*s)[a]
>>>> }
>>>> }
>>>>
>>>> On Tuesday, December 6, 2022 at 6:54:38 PM UTC-8 hey...@gmail.com
>>>> wrote:
>>>>
>>>>> Thanks for the quick reply.
>>>>>
>>>>> But that seems to compare values. I'd like to compare index numbers.
>>>>> The fact that original values follow index number order is a coincidence.
>>>>>
>>>>> > I think it'd be recommended to look at the generics slices package,
>>>>> which also has a sort
>>>>>
>>>>> Do you mean golang.org/x/exp/slices? That also seems to only compare
>>>>> values.
>>>>>
>>>>>
>>>>> On Wednesday, December 7, 2022 at 10:45:33 AM UTC+8 harr...@spu.edu
>>>>> wrote:
>>>>>
>>>>>> Subtly:
>>>>>> return s[i] > s[j]
>>>>>>
>>>>>> Is the right sort func
>>>>>>
>>>>>> I think it'd be recommended to look at the generics slices package,
>>>>>> which also has a sort
>>>>>> On Tuesday, December 6, 2022 at 6:39:29 PM UTC-8 hey...@gmail.com
>>>>>> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> I have this very simple sorting code:
>>>>>>>
>>>>>>> s := make([]int, 0, 100)
>>>>>>> for i := 1; i <= 20; i++ {
>>>>>>> s = append(s, i)
>>>>>>> }
>>>>>>> sort.Slice(s, func(i, j int) bool { return i > j })
>>>>>>> log.Print(s)
>>>>>>>
>>>>>>> I expect it to print numbers in reverse order, since items with
>>>>>>> larger index numbers should be at the front. However, at lease in
>>>>>>> go1.19.3,
>>>>>>> it prints
>>>>>>>
>>>>>>> [9 1 8 5 16 3 20 2 10 7 12 13 14 15 6 4 19 18 17 11]
>>>>>>>
>>>>>>> I guess I must have misunderstood how the sort package works, but
>>>>>>> rereading sort's doc multiple time doesn't help answer the question.
>>>>>>>
>>>>>>> Could anyone shed some light?
>>>>>>>
>>>>>>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/golang-nuts/57b141f1-a320-4e80-b646-890118552d9bn%40googlegroups.com.
