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MathGroup Archive 2008

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Re: Sorting 3 points

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87967] Re: [mg87935] Sorting 3 points
  • From: "Maarten van der Burgt" <maarten.vanderburgt at icos.be>
  • Date: Mon, 21 Apr 2008 06:37:44 -0400 (EDT)

Carlos,

This is the last of the 'basic examples' from the Help on Sort:

In:  Sort[{{a,2},{c,1},{d,3}},#1[[2]]<#2[[2]]&]

Out: {{c,1},{a,2},{d,3}}

The sorting function is

     #1[[2]]<#2[[2]]&

It should be easy to work out from this what you have to modify in this
sorting function to achieve the results you want.

Regards,

Maarten



                                                                                                                                               
                    carlos@Colora                                                                                                              
                    do.EDU               To:     mathgroup at smc.vnet.net                                                                        
                                         cc:                                                                                                   
                    21/04/2008           Subject:     [mg87935] Sorting 3 points                                                               
                    09:21                                                                                                                      
                                                                                                                                               
                                                                                                                                               




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.







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