Re: sort
- To: mathgroup at smc.vnet.net
- Subject: [mg29997] Re: [mg29991] sort
- From: BobHanlon at aol.com
- Date: Sat, 21 Jul 2001 00:49:04 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 2001/7/20 3:36:01 AM, nails at asu.edu writes:
>Does anybody now how to sort a matrix first by one column and then by
>another column (giving priority to the first column and sorting by
>second column only when there are ties in the first column).
>
sortByCol[l_List, n_Integer] :=
Sort[l, #1[[n]] <= #2[[n]]&];
mat = Table[Random[Integer, {1, 4}], {10}, {10}];
sortByCol[mat, 3]
To sort by column 3 with column 4 breaking ties
sortByCol[sortByCol[mat, 4], 3]
If more than two columns are to be used
Fold[sortByCol[#1, #2]&, mat, {5, 4, 3}]
Bob Hanlon
Chantilly, VA USA