CODEWITHSUNDEEP
matlabmultidimensional-array
user3026357
user3026357

Reputation: 25

sum in multidimensional arrays matlab

I have an I x K x V array, where V = S x R, ie, the third dimension has "S" observation for "R" different categories. I would like to end up with an I x K x S that has, in the third dimension, the sum across R within each S.

e,g: I = 3, K = 3, S=2 and R=2, I want to end up with a matrix C that is 3x3x2 that sums the third dimension in the following way.

A = [5 7 8; 0 1 9;4 3 6]; 
A(:,:,2)=[1 0 4; 3 5 6;9 8 7]
A(:,:,3)=[3 2 1 ; 4 5 6; 3 4 5]
A(:,:,4)=[1 2 3 ; 3 4 5; 5 6 7]
C=A(:,:,1)+A(:,:,2)
C2=A(:,:,3)+A(:,:,4)
C(:,:,2)=C2

I cannot do this manually b/c R and S are very large in my "real" case.

Thanks!

Upvotes: 1

Views: 2513

Answers (1)

Luis Mendo
Luis Mendo

Reputation: 112659

Separate the S and R dimensions with reshape, and then sum across the third dimension, which is S:

I = 3; K = 3; S = 2; R = 2;
C = squeeze(sum(reshape(A,[I K S R]),3));

If you want to sum across R, that's the fourth dimension:

C = sum(reshape(A,[I K S R]),4);

Upvotes: 1

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