how to build a 3d sparse matrix?

Question

UTA 2015-8-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/236976-how-to-build-a-3d-sparse-matrix

编辑： Lucademicus 2018-12-7

采纳的回答： Matt J

在 MATLAB Online 中打开

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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Answer 1

Matt J 2015-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/236976-how-to-build-a-3d-sparse-matrix#answer_190518

编辑：Matt J 2015-8-27

在 MATLAB Online 中打开

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 2018-12-6

编辑：Matt J 2018-12-6

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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 2018-12-7

编辑：Lucademicus 2018-12-7

Thank you for the suggestion, it greatly reduced the computational time!

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Answer 2

Steven Lord 2015-8-27

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https://ww2.mathworks.cn/matlabcentral/answers/236976-how-to-build-a-3d-sparse-matrix#answer_190508

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.