Re: Sorting 3 points
- To: mathgroup at smc.vnet.net
- Subject: [mg87980] Re: Sorting 3 points
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Mon, 21 Apr 2008 06:40:07 -0400 (EDT)
- Organization: University of Bergen
- References: <fuhfa6$ibk$1@smc.vnet.net>
carlos at colorado.edu wrote:
> Simple question, but documentation is no help.
> I have three coordinate triplets:
>
> P1={x1,y1,z1} P2={x2,y2,z2} P3={x3,y3,z3}
>
> where all entries are numeric. I wont to sort them into
>
> P1s={xs1,ys1,zs1} P2s={xs2,ys2,zs2} P3s={xs3,ys3,zs3}
>
> so that zs3>=zs2>=zs1, with one command
>
> {P1s,P2s,P3s}=Sort[{P1,P2,P3}, Ordering Function]
>
> Is that possible and if so, which Ordering Function
> should be used? Thanks.
Well, this is pretty simple if you read what an ordering function is ...
Sort[list, Last[#1] < Last[#2] &]
(Or if you have Mathematica 6, just use SortBy[list, Last])
Perhaps the missing piece was constructing anonymous functions? Read
the doc page of Function for an explanation (#1, #2 are the first and
second arguments of the function).