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MathGroup Archive 2005

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Re: position of letters in a string

  • To: mathgroup at smc.vnet.net
  • Subject: [mg53838] Re: [mg53803] position of letters in a string
  • From: János <janos.lobb at yale.edu>
  • Date: Sat, 29 Jan 2005 06:02:46 -0500 (EST)
  • References: <200501280743.CAA00311@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Jan 28, 2005, at 2:43 AM, zak wrote:



> in the list of strings:
> lst={"catcatz","zrzttys"}
> i want some procedure to give the letters in every string a number
> depending on its position and discarding the recurrent letters such
> that:
> first string: c=1; a=2; t=3; z=4
> second string: z=1; r=2; t=3; y=4; s=5
> zak
>
In the Help of Union there is an UnsortedUnion function. I use that one 
here.

In[22]:=
lst = {"catcatz", "zrzttys"}
Out[22]=
{"catcatz", "zrzttys"}

In[26]:=
UnsortedUnion[x_] :=
  Module[{f},
  f[y_] := (f[y] = Sequence[
  ]; y); f /@ x]; In[47]:=
lst1 = (UnsortedUnion[
  Characters[#1]] & ) /@
  lst
Out[47]=
{{"c", "a", "t", "z"},
  {"z", "r", "t", "y", "s"}}

In[66]:=
pairedLst = First[
  Last[Reap[While[lst1 =!=
  {}, current =
  First[lst1];
  lst1 = Rest[lst1];
  Sow[({#1, Flatten[
  Position[current,
  #1]]} & ) /@
  current]; ]]]]
Out[66]=
{{{"c", {1}}, {"a", {2}},
  {"t", {3}}, {"z", {4}}},
  {{"z", {1}}, {"r", {2}},
  {"t", {3}}, {"y", {4}},
  {"s", {5}}}}

I am sure there are shorter versions. Flatten is not needed if you need 
their Positions right away.

János



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