CODEWITHSUNDEEP
matlabfor-loopsum
user3482383
user3482383

Reputation: 295

Summing a 4D matrix without for loops in matlab

I have a 4D matrix A of size m × n × p × q. Consider B = A(:,:,1,1) which is an m × n matrix. I want to sum all the elements of B to give a number. I want to do this for all such B matrices for all A so finally I will have a p by q matrix.

How can i do this without for loops?

As an example for a 3D matrix (for example A be a 3D matrix) I think this works, 

sum(squeeze(sum(A,1)),1)

But I don't know how to do this for a 4D matrix...

Upvotes: 2

Views: 514

Answers (2)

Rody Oldenhuis
Rody Oldenhuis

Reputation: 38032

Probably fastest: 

permute(sum(sum(A)), [3 4 1 2]);

EDIT: nope, Shai's first solution is faster :)

Upvotes: 2

Shai
Shai

Reputation: 114816

what's wrong with

[m n p q] = size( A );
squeeze( sum( reshape( A, [], p, q ), 1 ) )

Alternatively,

squeeze( sum( sum( A, 2 ), 1 ) )

Upvotes: 3

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