MATLAB Answers

Mean of the third dimension

Hi I an new to matlab and learning thru practice and patience. I have a data set with for precipitation containing data for 37 years. X=141, Y=41 and T=37. I want to get the mean per year (37) I tried the following code but on my dataset I ended uo with 71 observations. Why this is happening? If I only want the mean per year? Thanks in advance.
avg3=nanmean(rain(:,:,3));

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Answer by John D'Errico
on 23 Oct 2019
Edited by John D'Errico
on 23 Oct 2019
 Accepted Answer

Not entirely sure what you are asking.
Do you want to compute the mean for each year for each combination of X and Y? That would result in a 141x41 array.
MeanRain = mean(rain,3);
Do you want to compute the mean over all X and Y, resulting in one element per year, so a vector of length 37? Here, I'd just reshape the rain matrix to be a 141*41 by 37 array, so 2-dimensional. Then take the mean down the columns of that array, so on the first dimension. The result of the computation below would be a 1x37 vector.
MeanRain = mean(reshape(rain,[],37),1);
Either could be what you are asking.

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Sorry if I was not clear enough. My goal is to achieve one mean ( point) per year. In total I want 37 averages one per year. After that I want to calculate the zscore per year to be able to do a time series.

John D'Errico
on 24 Oct 2019
Then you just use the second option I gave.

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Answer by TADA
on 23 Oct 2019
Edited by TADA
on 23 Oct 2019

try this:
avgPerYear = nanmean(rain, [1,2]);
that would generate an inconvenient 3rd dimention vector
so you can reshape it into a row\column vector:
avgPerYear = reshape(nanmean(rain, [1,2]), size(rain,3), 1, 1); % column vector output
avgPerYear = reshape(nanmean(rain, [1,2]), 1, size(rain,3), 1); % row vector output

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