MATLAB: Use only defined 4D array elements

4d arrayarray

Hello to All, There is 4D array varcov (NxNxZxL), I need to make other 4D array with the following values:
varcov1=[varcov(1,1,:,:) varcov(2,2,:,:) varcov(3,3,:,:) ..till end(N)];
That result varcov1 would be (1xNxZxL).

Best Answer

The code below should work for you. Since R2016b you can use the line with implicit expansion.
N=3;Z=4;L=6;
varcov=reshape(1:(N*N*Z*L),N,N,Z,L);%generate sample data
inds=bsxfun(@plus,(1:N+1:N^2)',N^2*(0:(Z*L-1)));%find the inds to the diagonal of each slice
%(1:N+1:N^2)'+N^2*(0:(Z*L-1)); with implicit expansion
varcov1=reshape(varcov(inds),1,N,Z,L);
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