Re: sorted?

On Mon, Dec 09, 2024 at 07:32:09PM +0100, Mikael Djurfeldt wrote:
> On Mon, Dec 9, 2024 at 2:11 PM <[email protected]> wrote:
> 
> > On Mon, Dec 09, 2024 at 01:58:08PM +0100, Mikael Djurfeldt wrote:
> >
> > [...]
> >
> > > No problem---I'm too.
> > >
> > > Think about it this way:
> > >
> > > How would you sort this list of numbers: 7 1 3 8 2 1 4 ?
> > >
> > > It's 1 1 2 3 4 7 8, right? That is what we want (sort '(7 1 3 8 2 1 4))
> > to
> > > output (+ the parentheses of course).
> > >
> > > Now, `sorted?' returns true if its input is what `sort' would have
> > produced
> > > as output, otherwise false.
> >
> > Hmmm. Perhaps, what throws me off the rails is that you can pass
> > a "less" predicate to sorted?.
> >
> > To behave like it does, it has to have some notion of equality,
> > which seems to be implicit and doesn't necessarily harmonize with
> > the less predicate you pass to it.
> >
> 
> (= a b) is equivalent to (not (or (< a b) (> a b)))

Yes, but for that, you have to know what "=" is. Is it eq? Is it
eqv? Is it equal? (yeah, lame pun with question marks). Or is it
(see below)?

> The reason why you need to pass less to sort is that sort needs a way to
> determine when an object should go before another one. Let's for example
> take the example of a list of neuronal spike events. Each event is (TIME .
> ID). It could be unsorted because the data might come from different
> detectors. To sort the list in time, we would call sort like this:
> 
> (sort '((0.73 . 7) (0.23 . 3) (0.54 . 17) (0.27 . 98)) (lambda (x y) (<
> (car x) (car y))))

So here you'd need your equal to be (eq (car x) (car y)), right?

[...]

> There is actually to kinds of `sort'. Ordinary sort and stable sort.

Yes, I know that -- but this wasn't my issue (or at least I think it
isn't).

Thanks for your patience :)

Cheers
-- 
t

-----BEGIN PGP SIGNATURE-----

iF0EABECAB0WIQRp53liolZD6iXhAoIFyCz1etHaRgUCZ1c+GgAKCRAFyCz1etHa
RibTAJ0V2SY2KCj94jilHbWBIyLfCC7KlwCcCwnMPry8eaPJDPJigUPZB5ghbVM=
=EcRQ
-----END PGP SIGNATURE-----