How to make a two-dimensional mask act on a three-dimensional array?

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Steve Francis
Steve Francis on 25 May 2022
Answered: Stephen23 on 26 May 2022
Here's a dummy three-dimensional array 'B' to illustrate the problem:
A = 9* ones (6,4,3); % create a 3 dimensional array
A(4,3,2)=NaN; % add a NaN
A(3,2,1)=NaN; % add another NaN;
B = A;
B is a 6x4x3 array with two NaN elements.
Wherever a NaN appears in array B, I want a NaN to overwrite all elements in the corresponding first dimension. So, in the example above, I want to convert B so that my output is
B(:,:,1) =
9 NaN 9 9
9 NaN 9 9
9 NaN 9 9
9 NaN 9 9
9 NaN 9 9
9 NaN 9 9
B(:,:,2) =
9 9 NaN 9
9 9 NaN 9
9 9 NaN 9
9 9 NaN 9
9 9 NaN 9
9 9 NaN 9
B(:,:,3) =
9 9 9 9
9 9 9 9
9 9 9 9
9 9 9 9
9 9 9 9
9 9 9 9
The script below appears to work but is not very elegant. Is there a way to do it without the 'for' loop?
% Here is my attempt to get NaN to overwrite all elements along the corresponding FIRST dimension
C = isnan(B); % create a logical mask
D = any (C,1); % look for any NaNs along the first dimension
for k=1:(size(B,1))
E=squeeze(B(k,:,:));
E(squeeze(D))=NaN; % apply the 'any' mask
B(k,:,:)=E ;
end
There is a very similar question here: https://uk.mathworks.com/matlabcentral/answers/358514-replace-all-the-array-with-nan-if-any-of-the-value-is-nan but I couldn't successfully tailor Jan's solution to my question. Thank you.

Answers (2)

Voss
Voss on 25 May 2022
Edited: Voss on 25 May 2022
You can replicate your matrix D=any(isnan(B),1) in the first dimension using repmat, generating a 3D logical array the same size as B, and then use that 3D logical array as a logical index in B:
A = 9* ones (6,4,3); % create a 3 dimensional array
A(4,3,2)=NaN; % add a NaN
A(3,2,1)=NaN; % add another NaN;
B = A;
B(repmat(any(isnan(B),1),[size(B,1) 1 1])) = NaN;
disp(B);
(:,:,1) = 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 (:,:,2) = 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 (:,:,3) = 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
  1 Comment
Steve Francis
Steve Francis on 25 May 2022
Thanks very much for your quick response. I wondered if there was any neat trick to do it by array multipication but your way works well.

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Stephen23
Stephen23 on 26 May 2022
"I wondered if there was any neat trick to do it by array multipication..."
A = 9* ones (6,4,3); % create a 3 dimensional array
A(4,3,2) = NaN; % add a NaN
A(3,2,1) = NaN; % add another NaN;
B = A
B =
B(:,:,1) = 9 9 9 9 9 9 9 9 9 NaN 9 9 9 9 9 9 9 9 9 9 9 9 9 9 B(:,:,2) = 9 9 9 9 9 9 9 9 9 9 9 9 9 9 NaN 9 9 9 9 9 9 9 9 9 B(:,:,3) = 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
X = 0./~any(isnan(B),1);
B = B+X
B =
B(:,:,1) = 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 B(:,:,2) = 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 9 9 NaN 9 B(:,:,3) = 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9
If you really want to use multilplication add 1 to X.

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