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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: [mg69538] Re: Summing elements within a List or Array
  • From: dimmechan at yahoo.com
  • Date: Fri, 15 Sep 2006 06:44:51 -0400 (EDT)
  • References: <eebfs6$57q$1@smc.vnet.net>

***You can work as follows:

In[96]:=
Flatten[Apply[Plus,alist,1],1]
Out[96]=
{0,1.2,3.5,6.9}

***or in compact form

In[95]:=
Plus@@@alist//Flatten
Out[95]=
{0,1.2,3.5,6.9}

***As you can see in the Help Browser and also in (Ted Ersek's Tips and
Tricks)
http://www.verbeia.com/mathematica/tips/HTMLLinks/Tricks_A-K_3.html

***(f@@lst)  is normally equivalent to Apply[f, expr] and  (f@@@lst)
is normally equivalent to Apply[f, lst, 1] as demonstrated below

In[103]:=
lst={1,2,3};

ln[104]:=
{Apply[f,lst]==f@@lst,Apply[f,lst,1]==f@@@lst}
Out[104]=
{True,True}

***BTW can you tell me how you generate your alist within Mathematica?


Dimitris Anagnostou


Î?/Î? John Adeosun έγÏ?αÏ?ε:
> 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.


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