# Sum subarrays of a Matrix.

10 vues (au cours des 30 derniers jours)
Santos García Rosado le 25 Fév 2021
Modifié(e) : Matt J le 26 Fév 2021
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
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### Réponse acceptée

Fangjun Jiang le 25 Fév 2021
Modifié(e) : Fangjun Jiang le 25 Fév 2021
One-liner
transpose(reshape(sum(reshape(A',3,[])),3,[]))
Or
transpose(cell2mat(cellfun(@sum,mat2cell(A',[3,3,3],3),'unif',0)))
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Fangjun Jiang le 25 Fév 2021
Can this task be done using accumarray()?? accumarray always makes my head spin!
Santos García Rosado le 26 Fév 2021
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!

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### Plus de réponses (1)

Matt J le 25 Fév 2021
Modifié(e) : Matt J le 26 Fév 2021
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Santos García Rosado le 26 Fév 2021
Nice function! I'm saving it for the future! Thanks Matt!

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