Re: Word permutations - frustrated by lists.

*To*: mathgroup at smc.vnet.net*Subject*: [mg71702] Re: Word permutations - frustrated by lists.*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Mon, 27 Nov 2006 04:04:10 -0500 (EST)*Organization*: The Open University, Milton Keynes, UK*References*: <ekbrks$jga$1@smc.vnet.net>

wooks wrote: > Hello. Am relatively new with Mathematica. > > I seem to have a general problem with results that look right but for > embedded lists. Here is an example of my problem. This is supposed to > be a algorithm to generate all permutations of a string. T > > Clear[arrangements] > arrangements[str_String /; StringLength[str] == 1] := {str}; > arrangements[str_String] := (Prepend[arrangements[StringJoin[ > Rest[#]]]], First[#]) & /@ > NestList[RotateRight, Characters[str], StringLength[str] - 1]; > arrangements["dear"] > > PS This is not homework. I'm rewriting some examples from another > programming book as as practice for Mathematica. > Hi, I am not sure which one is going to fit your needs (I admit I am a little bit confuse by your code and what I think you try to achieve.) Both are recursive functions, although the result given by the second function might not be what you had in mind. In[1]:= Clear[arrangements]; arrangements[str_String /; StringLength[str] == 1] := {str}; arrangements[str_String] := StringJoin /@ NestList[RotateRight, Characters[str], StringLength[str] - 1]; arrangements["dear"] Out[4]= {dear,rdea,arde,eard} In[5]:= Clear[arrangements]; arrangements[str_String /; StringLength[str] == 1] := {str}; arrangements[str_String] := (Prepend[arrangements[StringJoin[Rest[#1]]], First[#1]] & ) /@ NestList[RotateRight, Characters[str], StringLength[str] - 1]; arrangements["dear"] Out[8]= {{d,{e,{a,r},{r,a}},{r,{e,a},{a,e}},{a,{ r,e},{e,r}}},{r,{d,{e,a},{a,e}},{a,{d,e},{e,d}},{e,{a,d},{d,a}}},{ a,{r,{d,e},{e,d}},{e,{r,d},{d,r}},{d,{ e,r},{r,e}}},{e,{a,{r,d},{d,r}},{d,{a,r},{r,a}},{r,{d,a},{a,d}}}} HTH, Jean-Marc