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Re: Sort on vector component

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122026] Re: [mg122006] Sort on vector component
  • From: DrMajorBob <btreat1 at austin.rr.com>
  • Date: Sun, 9 Oct 2011 03:53:50 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201110080936.FAA21131@smc.vnet.net>
  • Reply-to: drmajorbob at yahoo.com

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

n = RandomChoice@Range@Last@Dimensions@u

3

SortBy[u, #[[n]] &]

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

u[[Ordering@u[[All, n]]]]

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

Bobby

On Sat, 08 Oct 2011 04:36:18 -0500, Dr. Wolfgang Hintze <weh at snafu.de>  
wrote:

> 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
>
>


-- 
DrMajorBob at yahoo.com



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