MATLAB Central Newsreader - how to sum elements with identical subscript

how to sum elements with identical subscript

vagrom Jiang — Sat, 29 Nov 2008 02:32:01 -0500

here is an example, A is N*2 matrix,
A = [2 20;
        5 10;
        5 30;
        7 10;
        .......];
expected result is A= [2 20;
                                5 40;
                                7 10;
                                .........];
how to solve this problem without any Loop to implement, since N could be very large, e.g 10e6.

Re: how to sum elements with identical subscript

John D'Errico — Sat, 29 Nov 2008 02:40:18 -0500

"vagrom Jiang" <vagrom@mytum.de> wrote in message <ggq9j1$ssm$1@fred.mathworks.com>...
> here is an example, A is N*2 matrix,
> A = [2 20;
> 5 10;
> 5 30;
> 7 10;
> .......];
> expected result is A= [2 20;
> 5 40;
> 7 10;
> .........];
> how to solve this problem without any Loop to implement, since N could be very large, e.g 10e6.
>

Consolidator does this. Find it here:

http://www.mathworks.com/matlabcentral/fileexchange/8354

HTH,
John

Re: how to sum elements with identical subscript

vagrom Jiang — Sat, 29 Nov 2008 02:57:01 -0500

That is so great! thanks a lot!

Re: how to sum elements with identical subscript

Roger Stafford — Sat, 29 Nov 2008 04:56:01 -0500

"vagrom Jiang" <vagrom@mytum.de> wrote in message <ggq9j1$ssm$1@fred.mathworks.com>...
> here is an example, A is N*2 matrix,
> A = [2 20;
> 5 10;
> 5 30;
> 7 10;
> .......];
> expected result is A= [2 20;
> 5 40;
> 7 10;
> .........];
> how to solve this problem without any Loop to implement, since N could be very large, e.g 10e6.

Or if you want to do it from scratch you can do it this way:

[t,m,n] = unique(A(:,1));
A = [t,accumarray(n,A(:,2))];

Roger Stafford