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Standard Deviation of 3D matrix with NaN elements

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António Rouxinol Fragoso
António Rouxinol Fragoso on 17 Sep 2019
Commented: Rik on 17 Sep 2019
I have a 3D matrix of size (170 x 170 x 27). Some of the entries are NaN, zero and the rest have real values.
I would like to obtain the standard deviation of this matrix, excluding the NaNs. I have tryed several commands, but I haven't been able to get this to work.
Could you help me?
Thank you in advance,
Antonio :)

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Answers (2)

Johannes Fischer
Johannes Fischer on 17 Sep 2019
As described in the doumentation for std, there is a flag on how to deal with 'NaN' values. If you want the standard deviation of all values, excluding the NaNs, then write
% dummy matrix
m=rand(170, 170, 27);
m(m>0.9) = NaN;
sdev = std(m, 0, 'all', 'omitnan')

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Rik
Rik on 17 Sep 2019
What release are you using? In previous releases the syntax for this function was slightly different.
Rik
Rik on 17 Sep 2019
The 'all' syntax was introduced in R2018b, so you'll have to linearize your array like I describe in my answer. doc for R2018a, doc for R2018b

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Rik
Rik on 17 Sep 2019
This syntax should work for most releases:
sdev=std(m(:),'omitnan');

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