Use only defined 4D array elements

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Mantas Vaitonis 2018-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/411548-use-only-defined-4d-array-elements

评论： Mantas Vaitonis 2018-7-22

采纳的回答： Rik

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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).

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Answer 1

Rik 2018-7-22

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https://ww2.mathworks.cn/matlabcentral/answers/411548-use-only-defined-4d-array-elements#answer_329823

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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);