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Standard deviation of a 3-d matrix

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Andrea
Andrea 2012-7-13
hi I have a matrix with size(y)=(200*1*4). I want to calculate the std for each (200*1) vector separately. When I used "std(y(y>0)), it gave me an value but I want in fact 4 values for each 200*1 vector size. How can I write the code to give me the std for each inner vector without "for",and ....
Thanks for your help

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Kye Taylor
Kye Taylor 2012-7-13
If y is 200-by-1-by-4, you can get rid of the singleton dimension using
y2D = squeeze(y);
then compute the 4 different standard deviations using
the4Sigmas = std(y2D);
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Kye Taylor
Kye Taylor 2012-7-13
编辑：Kye Taylor 2012-7-13
Sure, but next time, ask a brand new question.
I would then use a for loop
sigmasPositive = zeros(1,4);
for j = 1:size(y2D,2)
idxOfInterest = y2D(:,j) > 0;
sigmasPositive(j) = std(y2D(idxOfInterest,j));
end
or you can avoid the loop using
z = mat2cell(y2D,size(y2D,1),ones(1,size(y2D,2)));
sigmasPositiveNoLoop = cellfun(@(c)std(c(c>0)),z);
Andrea
Andrea 2012-7-13
Thanks a lot. I've already done that. but a little late. It works perfectly.

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