[Tutor] sorting objects on two attributes

[Chris Fuller]

Almost.  And better than my original idea.  You could have a hierarchical sort 
function:

def hiersort(a,b):
   if a.attr1 != b.attr1:
      return cmp(a.attr1, b.attr1)
   else:
      if a.attr2 != b.attr2:
         return cmp(a.attr2, b.attr2)
      else:
         return cmp(a.attr3, b.att3)


l.sort(hiersort)

You can keep nesting for more than three attributes, or you could make it 
arbitrary by setting it up recursively and setting the attribute hierarchy as 
a parameter somewhere.  But that's probably unnecessarily fancy.

Cheers

On Monday 03 March 2008 08:42, Andreas Kostyrka wrote:
> Well, this assumes that all named attributes do exist. If not, you need
> to replace x.attr with getattr(x, "attr", defaultvalue) ;)
>
>
> l.sort(key=lambda x: (x.content_type, x.submit_date))
>
> Now, you can construct a sorted list "t":
>
> t = []
> for key, item_iterator in itertools.groupby(l, key=lambda x:
> (x.content_type, x.submit_date)): sorted_part = sorted(item_iterator,
> key=lambda x: x.submit_date) t.append((sorted_part[-1].submit_date, key,
> sorted_part))
>
> t.sort()
>
> t = sum([x[2] for x in t], [])
>
> Totally untested, as written in the MTA :)
>
> Andreas
>
> Am Montag, den 03.03.2008, 22:19 +0800 schrieb Eric Abrahamsen:
> > I have a grisly little sorting problem to which I've hacked together a
> > solution, but I'm hoping someone here might have a better suggestion.
> >
> > I have a list of objects, each of which has two attributes, object_id
> > and submit_date. What I want is to sort them by content_type, then by
> > submit_date within content_type, and then sort each content_type block
> > according to which block has the newest object by submit_date. (This
> > sequence of sorting might not be optimal, I'm not sure). I'm actually
> > creating a list of recent comments on blog entries for a python-based
> > web framework, and want to arrange the comments according to blog
> > entry (content_type), by submit_date within that entry, with the
> > entries with the newest comments showing up on top.
> >
> > I don't believe a single cmp function fed to list.sort() can do this,
> > because you can't know how two objects should be compared until you
> > know all the values for all the objects. I'd be happy to be proven
> > wrong here.
> >
> > After some false starts with dictionaries, here's what I've got.
> > Queryset is the original list of comments (I'm doing this in django),
> > and it returns a list of lists, though I might flatten it afterwards.
> > It works, but it's ghastly unreadable and if there were a more
> > graceful solution I'd feel better about life in general:
> >
> >
> > def make_com_list(queryset):
> >     ids = set([com.object_id for com in queryset])
> >     xlist = [[com for com in queryset if com.object_id == i] for i in
> > ids]
> >     for ls in xlist:
> >         ls.sort(key=lambda x: x.submit_date)
> >     xlist.sort(key=lambda x: max([com.submit_date for com in x]),
> > reverse=True)
> >     return xlist
> >
> > I'd appreciate any hints!
> >
> > Thanks,
> > Eric
> > _______________________________________________
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