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RE: Sort on vector component

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122019] RE: [mg122006] Sort on vector component
  • From: Richard Hofler <rhofler at bus.ucf.edu>
  • Date: Sun, 9 Oct 2011 03:52:34 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110080936.FAA21131@smc.vnet.net>

Hello,

The answer that I believe you are looking for is given in the 3rd Basic Example in the Sort documentation:

u={{2,12,7,21},{2,48,47,97},{4,42,41,87},{6,8,1,15},{6,12,9,27}};

Sort[u]                                                         (* sort on 1st element in each sublist *)
Sort[u,#1[[2]]<#2[[2]]&]                            (* sort on 2nd element in each sublist *)
Sort[u,#1[[3]]<#2[[3]]&]                                               (* etc. *)
Sort[u,#1[[4]]<#2[[4]]&]          
                                              
{{2,12,7,21},{2,48,47,97},{4,42,41,87},{6,8,1,15},{6,12,9,27}}
{{6,8,1,15},{6,12,9,27},{2,12,7,21},{4,42,41,87},{2,48,47,97}}
{{6,8,1,15},{2,12,7,21},{6,12,9,27},{4,42,41,87},{2,48,47,97}}
{{6,8,1,15},{2,12,7,21},{6,12,9,27},{4,42,41,87},{2,48,47,97}}

Richard Hofler
________________________________________
From: Dr. Wolfgang Hintze [weh at snafu.de]
Sent: Saturday, October 08, 2011 5:36 AM
To: mathgroup at smc.vnet.net
Subject: [mg122019] [mg122006] Sort on vector component

Given a list

u = {{2, 12, 7, 21}, {2, 48, 47, 97}, {4, 42, 41, 87},
{6, 8, 1, 15}, {6, 12, 9, 27}}

How can I sort it with respect to a given index position i=(1, ..., 4)?

For i=1 it is simply Sort, for the last one I could use

In[75]:=
Reverse /@ Sort[Reverse /@ u]
Out[75]=
{{6, 8, 1, 15}, {2, 12, 7, 21}, {6, 12, 9, 27},
{4, 42, 41, 87}, {2, 48, 47, 97}}

I don't want to go in the details of defining lexicographical order but
just obtain a sorting as described above.

Any ideas?

Thanks in advance.

Wolfgang



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