MATLAB: Creating a monthly average from a matrix

grpstats

My data, which has 30 years of monthly data, over a 2 degree grid of the globe:
>> whos KoppenA_prate
  Name                Size                    Bytes  Class     Attributes
    KoppenA_prate      90x180x360            23328000  single
Not every pixel has data, just the pixels that fit into Koppen classification A
>> sum(A(:))
ans =
     559
My question: Any ideas on how I could write a loop to create an average monthly value over the 30 years?
Thanks a bunch!

Best Answer

Just
 avgAllYears = mean(KoppenA_prate, 3) ;
where 3 is the dimension along which the mean must be computed. With that you get a 90x180 array of means over all times.
EDIT:
 siz = size(KoppenA_prate) ;
 avg = zeros(siz(1), siz(2), 12) ;
 for mId = 1 : 12
    avg(:,:,mId) = mean(KoppenA_prate(:,:,mId:12:end), 3) ;
 end
EDIT2: or, more efficient but more complicated
 siz = size(KoppenA_prate) ;
 buf = mean(reshape(KoppenA_prate, siz(1), 12*siz(2), []), 3) ;
 avg = reshape(buf, siz(1), siz(2), []) ;
Note: both produce a 90x180x12 array of monthly averages, were e.g. avg(:,:,5) is the average of 5th months over all years.
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