Remove sub-matrix if any col are all nan (3D matrix)

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Dave 2015-2-19

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评论： Dave 2015-2-19

Hi, In a 3D matrix, I have 4 sub-matrices of 3x3, like A below

A=[1 2 nan; 2 5 nan; 4 2 nan];
A(:,:,2)=[3 4 5; 4 nan nan; 2 3 4];
A(:,:,3)=[8 nan nan; 1 nan nan; 8 nan nan];
A(:,:,4)=[1 2 3; 6 7 8; 3 3 5];

I need a new matrix that EXCLUDES the cases where the columns of A are ALL nan. In the case above submatrices A1 and A3 should be excluded, and the new matrix, say B, should be

B(:,:,1)=[3 4 5; 4 nan nan; 2 3 4];
B(:,:,2)=[1 2 3; 6 7 8; 3 3 5];

I'd also need the id of the sub-matrices of A to be finally used in B, in this case 2 and 4.

Let me know if it's not clear thanks

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Answer 1

Image Analyst 2015-2-19

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Using the any() and all() functions I'm sure you'll be able to figure it out - you're a smart engineer. These are useful functions to learn about as they are used often. Here's one way to do it:

A=[1 2 nan; 2 5 nan; 4 2 nan];
A(:,:,2)=[3 4 5; 4 nan nan; 2 3 4];
A(:,:,3)=[8 nan nan; 1 nan nan; 8 nan nan];
A(:,:,4)=[1 2 3; 6 7 8; 3 3 5]
% Find out what slices need to be deleted.
for z = 1 : size(A, 3)
  deleteThisSlice(z) = any(all(isnan(A(:,:,z)), 1))
end
B = A(:, :, ~deleteThisSlice)