Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
1996
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 1996

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Re; Reordering lists?!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4570] Re: Re; Reordering lists?!
  • From: Hein Hundal <hundal at vicon.net>
  • Date: Fri, 16 Aug 1996 05:15:04 -0400
  • Organization: Core Capital
  • Sender: owner-wri-mathgroup at wolfram.com

Andre and Alain 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
> 
> <The original list>
> 
> gsub=Flatten[ColumnTake[gcsq,{4}]]
> {2, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2, 2, 1, 1, 3, 1, 1, 2, 1, 2, 1, 2, 1, 1,
> 1, 1, 2, 1, 2, 1, 3, 1,
>   2, 2, 1, 2, 1, 2, 3, 2, 4, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 2, 2, 1, 2, 1, 2,
> 3, 2, 2, 2, 1, 2, 1,
>   2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 2, 2, 2, 1}
> 
> <Frequencies of the list>
> 
> Frequencies[gsub]
> {{42, 1}, {34, 2}, {4, 3}, {1, 4}}
> 
> <The code that replaces them>
> 
> Do[If[gsub[[n]]==1,gsub[[n]]=4]||
> If[gsub[[n]]==2,gsub[[n]]=3]||
> If[gsub[[n]]==3,gsub[[n]]=2]||
> If[gsub[[n]]==4,gsub[[n]]=1],
> {n,1,Length[gsub]}]
> 
> <It doesn't work properly?!>
> 
> Frequencies[gsub]
> {{43, 1}, {38, 2}}
> 
> Of course the new list frequencies should be exactly opposite than the first
> one. Help please?!
> Thanks
> Andre Bindon
> Ablerta Hospital Edmonton

The function you have built works well for values of 3 and 4, but for a value of 1 (or 2), 
the clause If[gsub[[n]]==1,gsub[[n]]=4] converts the 1 into a 4 and returns the value 4.  If 
this clause returned True then the program would go on to the next value of n, but because 4 
is returned, the remaining If clauses are evaluated.  So, If[gsub[[n]]==4,gsub[[n]]=1] 
converts the 4 back into a 1.  To Fix your code, you could have the If[]'s return True when 
their test is true.   
Do[
If[gsub[[n]]==1,gsub[[n]]=4;True]||
If[gsub[[n]]==2,gsub[[n]]=3;True]||
If[gsub[[n]]==3,gsub[[n]]=2;True]||
If[gsub[[n]]==4,gsub[[n]]=1;True],
{n,1,Length[gsub]}]

There are many other ways to achieve the same goal.  For example:

gsub /. Table[ a -> (5-a), {a,4}]


Hein Hundal

==== [MESSAGE SEPARATOR] ====


  • Prev by Date: Re: Re: graphs to postscript
  • Next by Date: Re: Minors[]
  • Previous by thread: Re: Re; Reordering lists?!
  • Next by thread: Re: Re; Reordering lists?!