
Re: Re; Reordering lists?!
Posted:
Jul 30, 1996 3:02 AM


In article <4thaug$j6e@dragonfly.wolfram.com>, Andre and Alain <abindon@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_] := (5x); ).
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

