RE: Sorting with Infinity
- To: mathgroup at smc.vnet.net
- Subject: [mg23529] RE: [mg23513] Sorting with Infinity
- From: "David Park" <djmp at earthlink.net>
- Date: Tue, 16 May 2000 22:30:00 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
> From: Jack Goldberg [mailto:jackgold at math.lsa.umich.edu] To: mathgroup at smc.vnet.net > Hi group; > > I construct lists which may look like this > > {7,-2,-Infinity,Infinity,1} > > When this list is sorted by using Sort, I get > > {-2,1,7,-Infinity,Infinity} > > I would prefer, naturally, > > {-Infinity,-2,1,7,Infinity} > > This is easy to do if one doesn't care about elegance. Without > spelling out the obvious details, here are a few kludges: > > (1) Replace Infinity by 10^15, Sort then switch back to Infinity. > (2) Use Append and Prepend after Sort and deleting infinities. > (3) RotateRight after Sort and switch signs on infinities > > Anyone got a "cute" solution say by using a sorting function or > perhaps some arcane command unknown to mere mortals? > > Jack > Hi Jack, Use the second optional argument in Sort to supply a sort criterion. Sort[{7, -2, -Infinity, Infinity, 1}, #2 > #1 || #1 === -Infinity || #2 === Infinity & ] {-Infinity, -2, 1, 7, Infinity} David Park djmp at earthlink.net http://home.earthlink.net/~djmp/