Re: Sort on vector component
- To: mathgroup at smc.vnet.net
- Subject: [mg122014] Re: Sort on vector component
- From: "Chris Degnen" <degnen at cwgsy.net>
- Date: Sun, 9 Oct 2011 03:51:40 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <j6q647$p1v$1@smc.vnet.net>
To sort by the last position use SortBy[u, Last] and for other positions, say the third, use Ordering: u[[Ordering[u[[All, 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 > >