How to reshape matrix without loop?

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John
John le 26 Juil 2017
Modifié(e) : John le 26 Juil 2017
Want to rearrange the matrix A(a,b,c,d) to B(b,c1,c2,d,a), where a,b,c,d are dimensions, c=c1*c2. If known c1=3, for example, B should be:
[a,b,c,d]=size(A);
C=permute(A,[2,3,4,1]);
c2=fix(c/c1);
B=zeros(b,c1,c2,d,a);
for nc=1:c1
B(:,nc,:,:,:)=C(:,nc:c1:end,:,:);
end
Can it be done more elegantly and without the loop?

Réponses (1)

John D'Errico
John D'Errico le 26 Juil 2017
WTP? Effectively two lines, one more to get the size of A if you don't know it already.
[a,b,c,d] = size(A);
B = reshape(A,[a,b,c1,c/c1,d]);
B = permute(B,[2 3 4 5 1]);
There is no need to use fix, because if c is not exactly divisible by c1, then A won't have the correct number of elements for a reshape anyway.
  1 commentaire
John
John le 26 Juil 2017
Modifié(e) : John le 26 Juil 2017
Hi, John: Will this make the dimension c1 to be the index (1,4,7,10...),(2,5,8,11...), (3,6,9,12...) from c respectively? Thanks.

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