MATLAB: Selection months (winter) in a matrix

datetimesteptime serieswinter

Hi all,
I have some problems with my datas. I have a matrix of 20x6x12x32 where 20 and 6 are the longitude and latitude, 12 the months and 384 the years.
I need to select the winter months like DJF, so I need the december of the previous year. For the first year I will obtain a winter just with JF and for the last year just with December.
I try this 
winter = wind(:,:,[12,1,2],:);
for i=1:20
    for j=1:6
        for k=1:3
            for z=1:32              
winter_mean(i,j,z)=mean(winter(i,j,k,z));
            end
        end
    end
end
But the result is incorrect because it choose the December of that year and not the previous one.
Any ideas?? Thank you really much

Best Answer

maxyear_to_calculate = 32;
winter = permute(wind(:,:,[12,1,2],:), [3 1 2 4]);  %month, long, lat, year
nyear = size(winter,4);
max_middle_year = min(maxyear_to_calculate, nyear);
for i=1:20
    for j=1:6
       z = 1;
       winter_mean(i, j, z) = mean(winter(2:3, i, j, z));  %first year has no december
       for z = 2 : max_middle_year           
          winter_mean(i,j,z) = mean([winter(1, i, j, z-1); winter(2:3, i, j, z)]);
       end
       if maxyear_to_calculate == nyear+1
         z = maxyear_to_calculate;
         winter_mean(i,j,z) = winter(1, i, j, z-1);   %last year has only december
       end
    end
end
Here, you should set maxyear_to_calculate to 384+1 = 385 if you want the final year to be calculated for.
That is, I respected your only calculating to 32, but at the same time putting in the full logic to calculate for the final year. The final entry is an extra entry; for example if you had data for 1970 1971 1972 then the entries would be based upon (JF 1970), (D 1970, JF 1971), (D 1971, JF 1972), (D 1972) for a total of 4 entries for data years.
The permute() was added to make it easier to calculate the means: without that re-arrangement, winter(i,j,2:3,z) would be 1 x 1 x 3 x 1 and I didn't want to bother with mean(cat(3,winter(i,j,1,z-1),winter(i,j,2:3,z)),3) so I moved the months to the first dimension.
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