how to build a 3d sparse matrix?

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UTA
UTA 2015-8-27
编辑： Lucademicus 2018-12-7
Hi everyone: As we all know these has a sparse function in matlab, for example, there has two vector:
a = [1 2 3 1 5]; b=[1 2 4 1 6];
if I use spase function like this as follow:
sn = sparse(a,b,1);
It will shows the answer like this:
ans =
(1,1) 2
(2,2) 1
(3,4) 1
(5,6) 1
the third column means the count number of conresponding row and column in a and b. So my qusetion is if it is possible to build a 3d sparse matrix as the extend of the trandtional sparse function as follow: if there has two vector:
aa = [1 2 1 1 2 3]; bb=[1 2 1 1 2 4];cc=[1 2 1 1 2 5];
snn = sparse_3d(aa,bb,cc,1);
snn=
(1, 1, 1) 3
(2, 2, 2) 2
(3, 4, 5) 1
That is very nice of anyone can give me the answer. Thanks ahead! weihua

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采纳的回答

Matt J
Matt J 2015-8-27
编辑：Matt J 2015-8-27
You could try my ndSparse class ( Download ),
>> snn = ndSparse.build([aa',bb',cc'],1)
snn(:,:,1) =
(1,1) 3
snn(:,:,2) =
(2,2) 2
snn(:,:,5) =
(3,4) 1
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Matt J
Matt J 2018-12-6
编辑：Matt J 2018-12-6
You can do that, but the more efficient way is to use ndSparse.build,
T=numel(time);
X=numel(x_vector);
Y=numel(y_vector);
coordinates=cell(T,1);
values=cell(T,1);
for t = 1:T
....somecalculations...
coordinates{t}=[xindices(:), yindices(:), xindices(:)*0+t];
values{t}=aboveresults(:);
end
coordinates=cell2mat(coordinates);
values=cell2mat(values);
AllResults = ndSparse.build(coordinates,values,[X,Y,T],NNZestimate);
Lucademicus
Lucademicus 2018-12-7
编辑：Lucademicus 2018-12-7
Thank you for the suggestion, it greatly reduced the computational time!

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更多回答（1 个）

Steven Lord
Steven Lord 2015-8-27
No, sparse matrices are limited to 2 dimensions. If you feel strongly that MATLAB should extend sparse matrices to 3 or more dimensions, please send your use case (how you would use those higher dimensional sparse arrays) to Technical Support and ask them to include that information in the enhancement database.

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