Re: Sort on vector component
- To: mathgroup at smc.vnet.net
- Subject: [mg122015] Re: Sort on vector component
- From: "Chris Degnen" <degnen at cwgsy.net>
- Date: Sun, 9 Oct 2011 03:51:51 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
> To sort by the last position use SortBy[u, Last]
> and for other positions, say the third, use Ordering:
> u[[Ordering[u[[All, 3]]]]]
or, alternatively, SortBy[u, #[[3]] &]
>
> Dr. Wolfgang Hintze 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
>>
>>