[Haskell-beginners] nub... almost

Iustin Pop iusty at k1024.org
Sat Jun 4 10:20:01 CEST 2011

On Fri, Jun 03, 2011 at 11:49:01PM -0800, Christopher Howard wrote:
> On 06/03/2011 11:37 PM, Christopher Howard wrote:
> > Weird request: For a certain application, the "nub" function from
> > Data.List is exactly what I need... almost. Nub removes duplicates,
> > keeping the /first/ occurrence of each element. However, I need a
> > function that removes duplicates, keeping the /second/ occurrence of
> > each element. There wouldn't happen to be a function already that does
> > this, would there?
> > 
> > I'm working with a custom type which is a member of Eq, but some of the
> > data in the type is not used in the comparison. So it is important which
> > of the two "duplicates" are actually saved.
> > 
> I should qualify this: By "second" I mean "last". Of course, it is
> possible for there to be more than one duplicate of any given element in
> a list. E.g., if there are three identical elements in a list, I want
> the third one, not the second one.

In that case, can't you simply revert the list, nub it, then revert
again (i.e. reverse . nub . reverse)?


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