Why does probabililty distribution for 3D matrix not work with NaN values?

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Hanna H
Hanna H 2020-5-22
评论： Hanna H 2020-5-27
Hi,
I am trying to calculate the critical probability for each grid point in a 3D matrix. To do so I have some sample data, calculated a test statistic and tested with a small sample to calculate the probability distribution and critical probability (all worked fine). Now I tried the same for the whole dataset (all grid points) and it won't work anymore, the code seems to stop when there are NaN values. My plan is to perform the calculation for each data point along the third dimension and skip each grid point, which is filled with NaN. This is where I am stuck now! I have tried several ways to omit NaNs but it doesn't seem to work.
This is the part of my code:
%% 2) calculate critical probability (lambda) for each grid point
f = zeros(size(U_stat,1),size(U_stat,2),100);
xi = zeros(size(U_stat,1),size(U_stat,2),100);
lambda_x_neg= zeros(size(U_stat,1),size(U_stat,2));
lambda_x_pos=zeros(size(U_stat,1),size(U_stat,2));
nonanlocs = ~isnan(U_stat);
for i = 1: size(U_stat,1)
for j = 1:size(U_stat,2)
[f(nonanlocs(i,j,:)),xi(nonanlocs(i,j,:))]=ksdensity(squeeze(U_stat(nonanlocs(i,j,:))));
% then calculate critical value lambda x for each grid point
lambda_x_neg(i,j) = xi(i,j,(find(f(i,j,:)<=0.05 & xi(i,j,:)<=0,1,'last')));
lambda_x_pos(i,j) = xi(i,j,(find(f(i,j,:)<=0.05 & xi(i,j,:)>0,1,'first')));
end
end
Many thanks for your help in advance!

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采纳的回答

darova
darova 2020-5-23
Try this way
%% 2) calculate critical probability (lambda) for each grid point
lambda_x_neg= zeros(size(U_stat,1),size(U_stat,2));
lambda_x_pos=zeros(size(U_stat,1),size(U_stat,2));
nonanlocs = ~isnan(U_stat);
f = U_stat*0;
xi = U_stat*0;
for i = 1: size(U_stat,1)
for j = 1:size(U_stat,2)
ix = nonanlocs(i,j,:)
[f(i,j,ix),xi(i,j,ix)] = ksdensity(squeeze(U_stat(i,j,ix)));
% then calculate critical value lambda x for each grid point
k1 = find(f(i,j,:)<=0.05 & xi(i,j,:)<=0,1,'last');
k2 = find(f(i,j,:)<=0.05 & xi(i,j,:)>0,1,'first');
lambda_x_neg(i,j) = xi(i,j,k1);
lambda_x_pos(i,j) = xi(i,j,k2);
end
end
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darova
darova 2020-5-24
Add if statements inside for loop
for i = 1: size(U_stat,1)
for j = 1:size(U_stat,2)
ix = nonanlocs(i,j,:)
if any(ix)
[f(i,j,ix),xi(i,j,ix)] = ksdensity(squeeze(U_stat(i,j,ix)));
% then calculate critical value lambda x for each grid point
k1 = find(f(i,j,:)<=0.05 & xi(i,j,:)<=0,1,'last');
k2 = find(f(i,j,:)<=0.05 & xi(i,j,:)>0,1,'first');
lambda_x_neg(i,j) = xi(i,j,k1);
lambda_x_pos(i,j) = xi(i,j,k2);
else
lambda_x_neg(i,j) = nan;
lambda_x_pos(i,j) = nan;
end
end
end
Hanna H
Hanna H 2020-5-27
Thanks a lot. I just had to change the index in the third dimension of the ouput variables f and xi in your suggestioned code and now its working!
[f(i,j,:),xi(i,j,:)] = ksdensity(squeeze(U_stat(i,j,ix)));

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更多回答（1 个）

KSSV
KSSV 2020-5-22
You can skip the computation using isnan. It gives you 1 as out put if number is nan and 0 if number is not a nan. Read about isnan.
if ~isnan(num)
% do what you want
end
You can also fill nan values using fillmissing. Or you can do inteprolation and get the values at the NaN's.

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