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MathGroup Archive 2006

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Re: Summing elements within a List or Array

  • To: mathgroup at smc.vnet.net
  • Subject: [mg69573] Re: Summing elements within a List or Array
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Fri, 15 Sep 2006 06:47:46 -0400 (EDT)
  • Organization: The Open University, Milton Keynes, UK
  • References: <eebfs6$57q$1@smc.vnet.net>

John Adeosun wrote:
> Hello Everyone,
> 
> I generated an intended list of real numbers using Mathematica 5.2, say 
> "alist", that looks like:
> 
> alist = {{0}, {{1.2},0}, {{2.3},{1.2},0},{{3.4},{2.3},{1.2},0}, 
> ................{{99.0},{98.9},{97.8},.......,0}}
> (In Matrix form, this "alist" can be shown as a LowerDiagonal Matrix)
> 
> Meanwhile, my present goal is to then program using Mathematica to obtain a 
> list, say "aalist", having each element equal to the sum of the elements in 
> each(corresponding) sublist of the original list "alist." That is,
> 
> aalist  = {0, 1.2, 3.5, 6.9,...........}
> 
> In essence, it is like reducing, say, 100 by 100 matrix to 100 by 1 matrix 
> via summing operation.
> 
>  I programmed using some summing operations/functions in Mathematica to no 
> avail. I don't know what I 'm doing wrong.
> 
> Can anyone help with this problem?
> 
> Thanks,
> 
> John. 
> 

alist = {{0}, {{1.2}, 0}, {{2.3}, {1.2}, 0}, {{3.4}, {2.3}, {1.2}, 0}, 
{{99.}, {98.9}, {97.8}, 0}};

aalist = Flatten[Apply[Plus, alist, {1}]]

--> {0, 1.2, 3.5, 6.9, 295.7}

Jean-Marc


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