Re: Re; Reordering lists?!

*To*: mathgroup at smc.vnet.net*Subject*: [mg4541] Re: Re; Reordering lists?!*From*: earhart at athena.mit.edu (Elizabeth J Earhart)*Date*: Wed, 7 Aug 1996 04:17:47 -0400*Organization*: Massachvsetts Institvte of Technology*Sender*: owner-wri-mathgroup at wolfram.com

In article <4thaug$j6e at dragonfly.wolfram.com>, Andre and Alain <abindon at gpu.srv.ualberta.ca> wrote: > Hey! I have a list of Numbers, 1 to 4, and wish to rescale them so >that 1 replkaces 4 and 3 replaces 2 and 2 replaces 3 etc. I made a little >code to do this on an element per element basis and it doesn't seem to do >it! Could someone let me know what I'm doing wrong or whether it's a Mma >problem? Thanks > [nonworking code snipped] The problem is that when you encounter 1's or 2's, you're changing them into 4's or 3's respectively, and then you hit the next If[] statement and change them back again! The easiest way to accomplish what you want is newgsub = (5-#)& /@ gsub; ('/@' is shorthand for Map[], '(5-#)&' is a pure function equivalent to f[x_] := (5-x); ). If you're not always going to be doing your substitution in such a way that the numbers add up to a constant, you can define an encoding function as follows: encode[x_] := Switch[x, 1, 4, 2, 3, 3, 2, 4, 1, _, x]; (That last line isn't absolutely necessary - it leaves unchanged anything that doesn't match any of the defined cases). Then you will get the correct result if you do newgsub = encode /@ gsub; (Equivalently, newgsub = Map[encode, gsub, {1}];) -Elizabeth ==== [MESSAGE SEPARATOR] ====