lcd wrote:
> > > On 21 March 2014, Cade Forester <[email protected]> wrote:
> > > > > How about separating it from sort()? That is, an uniq()
> > > > > function that would remove duplicates from an already sorted
> > > > > list (results would be undefined if the input list is not
> > > > > sorted). That would be consistent with how uniq(1) works on
> > > > > UNIX.
> > > >
> > > > This patch add uniq() function. uniq(list) will remove copies of
> > > > repeated adjacent items
> > >
> > > There is a problem with this patch: it removes the duplicates
> > > on the fly, so if the comparison function fails on the second or
> > > subsequent call the list is still modified. In contrast, sort()
> > > restores the list to the initial state if the comparison fails at
> > > some point.
> > >
> > > I'm attaching bellow my attempt to a fix. I also merged
> > > f_sort() and f_uniq() in a single function, and made some minor
> > > optimisations.
> > >
> > > On a related topic: adding an efficient "stable unique" would be
> > > relatively straightforward too, using plain red-black trees. Now,
> > > red-black trees are implemented as a header (namely sys/tree.h) on
> > > *BSD, but not on other systems. Any comment on the preferred way to
> > > handle this? I'd suggest testing for the existence of sys/tree.h in
> > > autoconf, and also including a stripped down copy of it from, say,
> > > OpenBSD, for the systems that don't have it.
> >
> > There are a few problems with this implementation.
> >
> > The li_prev pointer is not updated.
>
> Right: this comes from the initial patch. I should have checked
> what is actually going on.
>
> > When the first item is not a list the error is for sort(), even when
> > uniq() is used.
>
> Updated patch below.
Thanks. There are a few remaining issues but it's easier to fix them
than to explain the problems.
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