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