How to remove null matrices from a multidemensional array?

Question

Luciano Campos 2021-6-10

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评论： Luciano Campos 2021-6-10

Hi, I'd like to remove all null matrices from a 3-dimensional array.

Suppose I have the following 3x3x5 multidimensional matrix, where the first and the third matrices are null. ¿How can I remove the null matrices such that the resulting multidimensional matrix is 3x3x3?

Matrix(:,:,1) =

0 0 0

Matrix(:,:,2) =

-0.6842 0.8145 0.7498

0.8353 1.5250 0.0004

-1.5288 0.4317 1.3572

Matrix(:,:,3) =

0 0 0

Matrix(:,:,4) =

1.4528 0.0807 0.3814

-0.1675 -0.7258 1.0134

-0.1237 -0.3353 0.6182

Matrix(:,:,5) =

1.2482 0.1368 0.8166

0.8369 1.8682 -0.6398

-1.0774 -1.1223 0.8522

Thanks for your help!

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Answer 1

Max Heiken 2021-6-10

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编辑：Max Heiken 2021-6-10

在 MATLAB Online 中打开

You could identify the all zero pages and remove them like this:

Matrix(:, :, ~any(Matrix, [1, 2])) = [];

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Luciano Campos 2021-6-10

Thanks Max! This works just fine!

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Answer 2

Steven Lord 2021-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/853060-how-to-remove-null-matrices-from-a-multidemensional-array#answer_721800

在 MATLAB Online 中打开

Use the capability of the any function to accept a vector of dimensions over which to operate.

z = zeros(3);
r = @() rand(3);
M = cat(3, z, r(), z, r(), r())
M = 
M(:,:,1) =

     0     0     0
     0     0     0
     0     0     0


M(:,:,2) =

    0.5431    0.5116    0.6777
    0.3478    0.2512    0.9538
    0.9902    0.5727    0.1137


M(:,:,3) =

     0     0     0
     0     0     0
     0     0     0


M(:,:,4) =

    0.5013    0.7561    0.0333
    0.7886    0.6559    0.0514
    0.8881    0.1103    0.9360


M(:,:,5) =

    0.0428    0.5918    0.6839
    0.4889    0.5199    0.2981
    0.1230    0.2536    0.2200
whichPagesHaveData = any(M, [1 2])
whichPagesHaveData = 1×1×5 logical array
whichPagesHaveData(:,:,1) =

   0


whichPagesHaveData(:,:,2) =

   1


whichPagesHaveData(:,:,3) =

   0


whichPagesHaveData(:,:,4) =

   1


whichPagesHaveData(:,:,5) =

   1
M2 = M(:, :, whichPagesHaveData)
M2 = 
M2(:,:,1) =

    0.5431    0.5116    0.6777
    0.3478    0.2512    0.9538
    0.9902    0.5727    0.1137


M2(:,:,2) =

    0.5013    0.7561    0.0333
    0.7886    0.6559    0.0514
    0.8881    0.1103    0.9360


M2(:,:,3) =

    0.0428    0.5918    0.6839
    0.4889    0.5199    0.2981
    0.1230    0.2536    0.2200
isequal(M(:, :, 4), M2(:, :, 2)) % page 4 of M is page 2 of M2 by the way we constructed M
ans = logical
   1