Re: Permutations
- To: mathgroup at smc.vnet.net
- Subject: [mg65580] Re: Permutations
- From: bghiggins at ucdavis.edu
- Date: Sun, 9 Apr 2006 04:32:05 -0400 (EDT)
- References: <e12s2k$j79$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Peter,
Here is a fun way of doing it using regular expressions (new in 5.1).
Suppose we have a list of all the characters in the alphabet written as
a string , and we want to swap all pairs except h and r. Then we can
use a Regex expression with StringReplace:
StringReplace[str, RegularExpression["([^h,^r])(\w)"] :> "$2" ~~ "$1"]
Here is a specific example
char = CharacterRange["a", "z"]
myfunc[int1_, int2_] := Characters[StringReplace[StringJoin[char], \
RegularExpression["([^" <> ToString[char[[int1]]] <>
",^" <> ToString[char[[int2]]] <> "])(\w)"] :> "$2" ~~ "$1"]]
myfunc[7,20]
{b,a,d,c,f,e,g,i,h,k,j,m,l,o,n,q,p,s,r,t,v,u,x,w,z,y}
To swap all pairs we can use
Characters[StringReplace[StringJoin[char],
RegularExpression["(\w)(\w)"] :> \
"$2" ~~ "$1"]]
Cheers,
Brian