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MathGroup Archive 2011

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Sort on vector component

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122006] Sort on vector component
  • From: "Dr. Wolfgang Hintze" <weh at snafu.de>
  • Date: Sat, 8 Oct 2011 05:36:18 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

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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