Sum subarrays of a Matrix.

Hi Mathworks community! Could someone give me a hand?

I'm having trouble trying to sum parts of the arrays of a matrix. Let's say I have the following matrix A of r rows and c columns (rxc).

A = [1,2,3,4,5,6,7,8,9; 10,11,12,13,14,15,16,17,18; 19,20,21,22,23,24,25,26,27]

And what I would like to to is to divide each array in n subarrays (n=3) and sum each of those subarrays. In this case, it would be the sum of every three positions. Getting an output suchs as:

out = [5,15,24; 33,42,51; 60,69,78]

Thank's for the help!

Santos

Answer 1

[Fangjun Jiang]

One-liner

transpose(reshape(sum(reshape(A',3,[])),3,[]))

Or

transpose(cell2mat(cellfun(@sum,mat2cell(A',[3,3,3],3),'unif',0)))

[Fangjun Jiang]

Can this task be done using accumarray()?? accumarray always makes my head spin!

[Santos García Rosado]

I'm using this code for Simulink and the first answer your proposea works perfectly fine. However, Simulink seems not to like the function cell2mat you wrote on the second line but it does work okay with Matlab. Thank's for the help Fangjun!

Answer 2

[Matt J]

Using sepblockfun

https://www.mathworks.com/matlabcentral/fileexchange/48089-separable-block-wise-operations

out=sepblockfun(A,[1,3],'sum')

[Santos García Rosado]

Nice function! I'm saving it for the future! Thanks Matt!