[sage-devel] Re: Suspiciously sorted sets
Hi Rob!
On Sep 21, 2:15 am, Rob Beezer goo...@beezer.cotse.net wrote:
sage: g = Graph()
sage: g.add_vertices(Subsets(3,2))
sage: g.vertices()
[{2, 3}, {1, 2}, {1, 3}]
sage: sorted(g.vertices())
[{1, 3}, {1, 2}, {2, 3}]
sage: Subsets(3,2).list()
[{1, 2}, {1, 3}, {2, 3}]
sage: sorted(Subsets(3,2).list())
[{2, 3}, {1, 3}, {1, 2}]
I think the problem is that there is no proper ordering defined for
sage.sets.set.Set_object_enumerated:
sage: S = Subsets(3,2).list()[0]
sage: T = Subsets(3,2).list()[1]
sage: S
{1, 2}
sage: T
{1, 3}
sage: type(S)
class 'sage.sets.set.Set_object_enumerated'
sage: S T
True
sage: T S
True
sage: S==T
False
So, unless someone implements __cmp__ (or similar) methods for
Set_object_enumerated, you can't expect to get anything meaningful out
of the sorting.
Best regards,
Simon
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[sage-devel] Re: Suspiciously sorted sets
Hi!
On Sep 21, 10:22 am, Simon King simon.k...@nuigalway.ie wrote:
[...]
So, unless someone implements __cmp__ (or similar) methods for
Set_object_enumerated, you can't expect to get anything meaningful out
of the sorting.
If your question is just about getting *some* unique result (say, for
a doc test): You can sort the elements of your list first, and then
you have a list of list (rather than a list of sets) that you can sort
in a unique way.
sage: g = Graph()
sage: g.add_vertices(Subsets(3,2))
sage: g.vertices()
[{2, 3}, {1, 2}, {1, 3}]
sage: sorted([sorted(list(V)) for V in g.vertices()])
[[1, 2], [1, 3], [2, 3]]
sage: Subsets(3,2).list()
[{1, 2}, {1, 3}, {2, 3}]
sage: sorted([sorted(list(V)) for V in Subsets(3,2)])
[[1, 2], [1, 3], [2, 3]]
Cheers,
Simon
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[sage-devel] Re: Suspiciously sorted sets
Hi Simon, Thanks for the explanation and isolating the problem, plus the workaround for getting a unique result. I did have doctesting in the back of my mind, even though it is not necessary at the moment for the patch in question. I'll likely add to Trac a ticket about the need for a comparison method on sets later today when I get a chance. Rob --~--~-~--~~~---~--~~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org -~--~~~~--~~--~--~---
[sage-devel] Re: Suspiciously sorted sets
I'll likely add to Trac a ticket about the need for a comparison method on sets later today when I get a chance. Just for the record, sorted sets make very little sense. It is important to be able to have a set containing anything that is hashable (in the python sense) but not necessarily sortable (again in the python sense). If you can't sort the elements, how can you order the sets themselves? Nick --~--~-~--~~~---~--~~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org -~--~~~~--~~--~--~---
[sage-devel] Re: Suspiciously sorted sets
Hi Nick, On 22 Sep., 00:02, Nick Alexander ncalexan...@gmail.com wrote: Just for the record, sorted sets make very little sense. Sure. When I said unless something implements a __cmp__ method... I did not mean that one *should* implement it; I just wanted to explain sorted(...) relies on a __cmp__ method, so if in some context one wants sorted to work then __cmp__ must be implemented. In the case of sets, I totally agree that the user should transform the set into a list and then proceed with that, if s/he wants some orderable object. Best regards Simon --~--~-~--~~~---~--~~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org -~--~~~~--~~--~--~---
