Find maxima every n positions in 3D matrix

Hello! I have a 500x400x120 matrix. I need to get the maximum values of every 12 steps in the 3rd dimension, so to end up with a 500x400x10 matrix. I tried

max(matrix(:,:,1:12:end),[],3)

but it gives me a 500x400 matrix as a result. Any ideas? Thanks in advance!

[James Tursa]

Do you mean max of matrix(:,:,1:12) across the 3rd dimension being the first 2D matrix, then the max of matrix(:,:,13:24) across the 3rd dimension being the next 2D matrix, etc?

[Chris]

Yeah, exactly!

Answer 1

[Image Analyst]

Do that 10 times but with the indexes correct:

means = zeros(500, 400, 10);
for k = 1 : 10
    z1 = (k - 1) * 12 + 1;
    z2 = z1 + 11;
    means(:, :, k) = max(matrix(:,:, z1:z2), [], 3);
end

[Chris]

Thanks a lot!

Answer 2

[Kaushik Lakshminarasimhan]

Here's one with while loop. There's probably a faster way.

stepsize = 12; count = 1; i=1; 
while i<=size(mymatrix,3)
   mymaxmatrix(:,:,count) = max(mymatrix(:,:,i:i+stepsize-1),[],3); 
   count = count+1; i=i+stepsize; 
end

[Chris]

Does the job anyway, thanx!