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

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Steve Francis on 25 May 2022
Edited: Stephen23 on 16 Jul 2022
Here's a dummy three-dimensional array 'B' to illustrate the problem:
A = 9* ones (6,4,3); % create a 3 dimensional array
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.

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.
Stephen23 on 16 Jul 2022
Edited: Stephen23 on 16 Jul 2022
A = 9*ones(4,3,6); % create a 3 dimensional array
A(3,2,4) = NaN; % add a NaN
A(2,1,3) = NaN % add another NaN;
A =
A(:,:,1) = 9 9 9 9 9 9 9 9 9 9 9 9 A(:,:,2) = 9 9 9 9 9 9 9 9 9 9 9 9 A(:,:,3) = 9 9 9 NaN 9 9 9 9 9 9 9 9 A(:,:,4) = 9 9 9 9 9 9 9 NaN 9 9 9 9 A(:,:,5) = 9 9 9 9 9 9 9 9 9 9 9 9 A(:,:,6) = 9 9 9 9 9 9 9 9 9 9 9 9
B = A;
X = 0./~any(isnan(B),3);
B = B+X % ^ you just need to change this
B =
B(:,:,1) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9 B(:,:,2) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9 B(:,:,3) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9 B(:,:,4) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9 B(:,:,5) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9 B(:,:,6) = 9 9 9 NaN 9 9 9 NaN 9 9 9 9

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
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
##### 2 CommentsShowHide 1 older comment
Steve Francis on 16 Jul 2022
I've changed the orientation of the matrix and was hoping that you could advise on the revised repmat statement, please?
A = 9* ones (4,3,6); % create a 3 dimensional array
B = A;
The desired output is now
val(:,:,1) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
val(:,:,2) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
val(:,:,3) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
val(:,:,4) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
val(:,:,5) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
val(:,:,6) =
9 9 9
NaN 9 9
9 NaN 9
9 9 9
The following seems to work:
B(repmat(any(isnan(B),3),[1 1 size(B,3)])) = NaN;
Is that correct?

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