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MathGroup Archive 2006

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Re: how to sum lists of unequal length?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70381] Re: [mg70352] how to sum lists of unequal length?
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Sun, 15 Oct 2006 00:18:43 -0400 (EDT)
  • References: <200610140706.DAA07887@smc.vnet.net>

On 14 Oct 2006, at 16:06, Arkadiusz.Majka at gmail.com wrote:

> Hi all,
>
> I have lists of unknown and unequal lengths. I want to sum them, e.g
>
> {a1,a2,a3}+{b1,b2,b3,b4,b5} and obtain result
> {a1+b1,a2+b2,a3+b3,b4,b5}. Simply filling by zeros of the shorter list
> is impossible because I have no idea how many zeros I have to pad.
>
> Please, help
>
> Arek
>

One way:

AddLists[l_,m_]:=With[{
     p=Max[Length[l],Length[m]]},PadRight[l,p]+PadRight[m,p]]


AddLists[{a1,a2,a3},{b1,b2,b3,b4,b5}]

{a1+b1,a2+b2,a3+b3,b4,b5}

Andrzej Kozlowski
Tokyo, Japan


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