how to return indices?

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Lilya
Lilya on 12 Jun 2022
Commented: Lilya on 12 Jun 2022
Hi,
I have a 3 dimensional data matrix (72*45*2109), and I need to extract all data less than 15. the final output should be a 3d matrix
I used the following lines, but the result is a vector. The point is to return the indices to have 3d matrix.
Any help would be greatly appreciated.
[r,c,v] = ind2sub(size(data),find(data >= 15));
l = data(sub2ind(size(data),r,c,v));
  2 Comments
DGM
DGM on 12 Jun 2022
Edited: DGM on 12 Jun 2022
You get a vector, because those are the indices of elements that you wanted -- only the indices you wanted.
Arrays need to be rectangular, without holes.
With that restriction, you'll have to decide what you want to fill all the area where there are elements you didn't want. It could be zero, NaN, etc. It's up to you and what the subequent code can accept without causing errors, since neither zero nor NaN are valid indices.
Lilya
Lilya on 12 Jun 2022
thanks for your comment
I've created an output nan matrix with the same dimension (72*45*2109), but all the output (r,c,v) are vectros as well
I don't know how to put them back in the output matrix

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Accepted Answer

Dyuman Joshi
Dyuman Joshi on 12 Jun 2022
Based on your comment -
%random data
y=randi(30,2,3,4)
y =
y(:,:,1) = 7 17 10 24 11 14 y(:,:,2) = 3 2 6 13 17 1 y(:,:,3) = 26 3 14 26 27 3 y(:,:,4) = 7 5 4 3 7 26
z=NaN(2,3,4);
z(y<15)=y(y<15)
z =
z(:,:,1) = 7 NaN 10 NaN 11 14 z(:,:,2) = 3 2 6 13 NaN 1 z(:,:,3) = NaN 3 14 NaN NaN 3 z(:,:,4) = 7 5 4 3 7 NaN
  1 Comment
Lilya
Lilya on 12 Jun 2022
Thank you very much!!
perfectly worked.

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