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MathGroup Archive 2006

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Re: generalized foldlist problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69082] Re: [mg69057] generalized foldlist problem
  • From: "Christoph Lhotka" <lhotka at astro.univie.ac.at>
  • Date: Wed, 30 Aug 2006 06:32:04 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hi!

One prodcedural approach:

f[list1_,list2_]:=Plus@@Table[
      PadRight[
        Join[
          Table[0,{i-1}],
          Table[list1[[i]],
            {list2[[i]]}]],
        Length[list1]],
      {i,1,Length[list1]}]

one rule based approach:

f[list1_,list2_]:=Plus@@With[{dim=Length[list1]},
      SparseArray[
        {{i_,j_}:>list1[[i]]/;
              j<=list2[[i]]+i-1&&
                j>=Position[list1,list1[[i]]][[1,1]]
          },
        {dim,dim}]]

Both should work for lists of same length.

wkr christoph


On Tue, 29 Aug 2006 03:25:38 -0400 (EDT)
 "Arkadiusz Majka" <Arkadiusz.Majka at telekomunikacja.pl> wrote:
> DearAll,
> 
> Please, help!
> 
> I have two list
> 
> list1={a,b,c,d,e}
> list2={3,2,5,1,6}
> 
> and I want to apply a modified version of FoldList to list1 in the
> following way: list2 indicates that element a appears only 3 times (if
> space enough) beginning from the beginning of the list , element b
> appears 2 times, c - 5 times , etc.
> 
> So the output should be
> 
> GeneralizedFoldList[list1,list2]={a,a+b,a+b+c,c+d,c+e}
> 
> Thanks for any hints,
> 
> arek
> 

-- Mag. Christoph Lhotka --
University of Vienna / Institute for Astronomy
fon. +43 (1) 4277 51841
mail. lhotka at astro.univie.ac.at


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