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Re: Cyclic permutations

• To: mathgroup at smc.vnet.net
• Subject: [mg79461] Re: Cyclic permutations
• From: Peter Pein <petsie at dordos.net>
• Date: Fri, 27 Jul 2007 05:52:47 -0400 (EDT)
• References: <f7pon7$prc$1@smc.vnet.net> <f7sgu2$ss8$1@smc.vnet.net> <f84juv$qpq$1@smc.vnet.net> <200707250614.CAA23554@smc.vnet.net> <33340097.1185365315232.JavaMail.root@m35> <f89qar$5qm$1@smc.vnet.net>

DrMajorBob schrieb:
> For instance...
> 
> perms = {{a, b, c, d}, {a, c, b, d}, {b, c, d, a}};
> unsortedUnion[x_] := Tally[x][[All, 1]]
> unsortedUnion[perms /. {x__, a, y___} :> {a, y, x}]
> 
> {{a, b, c, d}, {a, c, b, d}}
> 
> Bobby
> 
> On Wed, 25 Jul 2007 04:27:37 -0500, King, Peter R  
> <peter.king at imperial.ac.uk> wrote:
> 
...
>> (by the way I am still using version 5.1 so V6 specific methods wouldn't
>> help I'm afraid)
>>

(*
  * Tally
  *)
Tally[Except[_List],f___]:={};

Tally[lst_List]:= (* this is faster for test===SameQ *)
    Block[{f},
      f[x_]:=(f[x]=Sequence[];{x,Count[lst,x,{1}]});
      f/@lst];

Tally[lst_List,f_]:=
    NestWhile[
        Block[{n=0},
            {DeleteCases[#[[1]],x_/;And[f[#[[1,1]],x],++n>0],{1}],
              Join[#[[2]],{{#[[1,1]],n}}]
              }]&,
        {lst,{}},#[[1]]=!={}&][[2]];

• References:
  • Re: Mathematica to .NET compiler
    • From: David Bailey <dave@Remove_Thisdbailey.co.uk>