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Standard deviation ignoring 0s in matrix

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Mate 2u
Mate 2u on 24 Jul 2012
Hi all, I have a 295x34 matrix called Absy. I want to take the standard deviation of all the columns, however some columns contain many zeros. I want to ignore the zeros and take the standard deviation (as zeros are only their due to some columns being different size).
Thank you.

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Accepted Answer

Matt Kindig
Matt Kindig on 24 Jul 2012
One easy way would be to convert all zeros to NaN, and then use the nanstd function to ignore the NaNs in the std calculation.
Absy(Absy==0)=NaN;
s = nanstd(Absy,[],1); %column by column std deviation

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Mate 2u
Mate 2u on 24 Jul 2012
Is their a way to do this with kurtosis also?

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More Answers (1)

Jan
Jan on 24 Jul 2012
Edited: Jan on 24 Jul 2012
x = rand(295, 34);
x(rand(size(x)) < 0.1) = 0;
index = (x ~= 0);
sumnz = sum(index, 1);
meanx = sum(x, 1) ./ sumnz;
xm = bsxfun(@minus, x, meanx);
xm(~index) = 0;
s = sqrt(sum(xm .* xm, 1) ./ (sumnz - 1));
[NOT TESTED]

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