CODEWITHSUNDEEP
matlabmatrix3d
Ehsan
Ehsan

Reputation: 517

create 3D (n:m:k) matrix in matlab using array 2D (i:3)

I need a 3D matrix in matlab, I have another 2D matrix (7570x3) too, The 3D matrix should have zero number except of all dimensions in 2D matrix that should have 1 value. How can I do that.

i.e. 2D matrix (1,:) = 28,64,27 then 3d(27,64,27) should be 1

how can i do that?

Upvotes: 0

Views: 258

Answers (2)

Ehsan
Ehsan

Reputation: 517

Thanks a lot @natan

for non-integer matrix also can use:

b=false(floor(max(a)));  % preallocate memory for a logical zeros matrix b
b(sub2ind(size(b),floor(a(:,1)),floor(a(:,2)),floor(a(:,3)))) = 1;

or use round function:

b=false(round(max(a)));  % preallocate memory for a logical zeros matrix b
b(sub2ind(size(b),round(a(:,1)),round(a(:,2)),round(a(:,3)))) = 1;

Upvotes: 0

bla
bla

Reputation: 26069

Assuming a is your 2-d matrix, and b is the 3-d one, use sub2ind as follows:

b=false(max(a));  % preallocate memory for a logical zeros matrix b
b(sub2ind(size(b),a(:,1),a(:,2),a(:,3))) = 1;

Check to see what max(a) gives you to see if you can host a 3-d matrix of size(max(a) to begin with. Since you are interested in a logcial matrix (ones and zeros), the size of that matrix in memory is the same as the # of elements, n*m*l, so a 1000x1000x1000 will take 1 GB.

Note, it very well may be that b is very sparse, if that is the case you can refer to this thread to see how to deal with it. Know that at the moment, and to the best of my knowledge, matlab doesn't support 3d sparse matrices. So you may want to check this option from the FEX. When I think of it, you already have a sparse look-up table of the 3D matrix! it is just your 2D matrix you started with...

Upvotes: 1

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