RE: Friendly Challenge 2: sort by column
- To: mathgroup at smc.vnet.net
- Subject: [mg35018] RE: [mg35005] Friendly Challenge 2: sort by column
- From: "Wolf, Hartmut" <Hartmut.Wolf at t-systems.com>
- Date: Thu, 20 Jun 2002 02:13:13 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
> -----Original Message----- > From: gleam at flashmail.com [mailto:gleam at flashmail.com] To: mathgroup at smc.vnet.net > Sent: Wednesday, June 19, 2002 11:53 AM > Subject: [mg35018] [mg35005] Friendly Challenge 2: sort by column > > > Once again, I am posting a friendly challenge with the hope of > provoking thought and encouraging creativity. This time, the > challenge is to write the "best" sort-by-column function you can. > > Once again, have already written several such > functions, which I will > delay posting these until a number of responses are received. This is > not because I think I am some kind of Mathematica "guru" will all the > right answers, but rather to prevent my methods from influencing > others. > > Once again, though I am setting guidelines for this > challenge, I will > not be pronouncing some final judgement of a winning algorithm. I > would much prefer that this challenge induces a good discussion of the > merits of various approaches and methods. > > Description: > > The function shall take two arguments: (1) a rectangular matrix and > (1) the number of a column in (1). > > The function shall sort the rows of (1) according primarily to the > element in the column specified by (2). > > The function shall not effect sub-elements in a three dimensional > matrix. > > Example: > > a = {{77,27,57,53}, > {72,21,40,27}, > {96,76,87,27}, > {61,97,93,71}, > {43,80,21,87}} > > In:= f[a, 3] > > Out= {{43,80,21,87}, > {72,21,40,27}, > {77,27,57,53}, > {96,76,87,27}, > {61,97,93,71}} > > You may handle duplicates in the sort column as you see fit, but > please explain it for the rest of us, and be prepared give support for > this as you would all other behaviors of your function. > > Be creative, have fun, and good luck! > > Paul > > Paul, a few quick ideas (leave testing up to you), unbundeled, unsorted: (1) Transpose[ RotateRight[Transpose[Sort[Transpose[RotateLeft[Transpose[a], 2]]]], 2]] (2) RotateRight[Sort[RotateLeft[a,{0,2}]],{0,2}] (3) Sort[a, #1[[3]] < #2[[3]] &] (4) a[[Ordering[Transpose[a][[3]]]]] -- Hartmut