Re: Custom sort a list of pairs
- To: mathgroup at smc.vnet.net
- Subject: [mg73662] Re: Custom sort a list of pairs
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sat, 24 Feb 2007 02:13:23 -0500 (EST)
- Organization: Uni Leipzig
- References: <ermdtt$i3t$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
Hi,
lst = {{1, a}, {2, a}, {3, a}, {1, b}, {2, b}, {1, c}};
Sort[lst,
If[#1[[1]] == #2[[1]], #1[[2]] > #2[[2]], #1[[1]] > #2[[1]]] &]
??
Regards
Jens
planetmarshalluk at hotmail.com wrote:
> Hi there,
>
> I've searched through existing posts to no avail, what I want to do is
> this:
> Sort a nested list of pairs, so that each pair is sorted by reverse
> canonical order on its first element, and in normal order on its
> second element.
>
> For example, I want some function
>
> sortPairs[items_]
>
> that when given the input
>
> {{ 1,a},{2,a},{3,a},{1,b},{2,b},{1,c}}
>
> produces the output
>
> {{3,a},{2,a},{2,b}{1,a},{1,b},{1,c}}
>
> Any help much appreciated.
>
> Thanks,
> Andrew
>
>