Append data to 3rd dimension in loop

I have 68 4320x2160x24 files that I use a for loop to read in and perform some tasks on, then I iteratively store output in a new variable. Towards the end of the script, I want to iteratively store the 4320x2160x12 matrix ndvi_mmax into a 4320x2160x(12*68) matrix (NDVI_monthmax). My current attempts have failed, I'm notsure whther I need to create a 4D matrix or if I need another, nested, loop, or convert to a cell. Any help appreciated.

startyear = 1982;
endyear = 2015;
nyears = length(startyear:endyear);
nmonths = nyears*12;
%Preallocate variables for output file
NDVI_mean = zeros(4320,2160,nyears); % mean annual NDVI
NDVI_monthmax = zeros(4320,2160,nmonths); % highest monthly mean NDVI
MD = zeros(4320,2160,nyears); % # of missing datapoints each year
%load data and define variables

for i = 1:nyears
    yr = (startyear-1)+i;

    filename1 = sprintf('ndvi3g_geo_v1_%d_0106.nc4', yr);
    filename2 = sprintf('ndvi3g_geo_v1_%d_0712.nc4', yr);
    fullFileName1 = fullfile(myFolder, filename1);
    fullFileName2 = fullfile(myFolder, filename2);

    ncid1 = netcdf.open(fullFileName1);
    ncid2 = netcdf.open(fullFileName2);
    %disp(filename1)

    %ncdisp(fullFilename1)
    NDVI1 = ncread(fullFileName1, 'ndvi');
    NDVI2 = ncread(fullFileName2, 'ndvi');
    flag1 = ncread(fullFileName1, 'percentile');
    flag2 = ncread(fullFileName2, 'percentile');
    
    NDVI = cat(3,NDVI1,NDVI2);
    NDVI = double(NDVI);
    NDVI(NDVI == -32768) = NaN;
    NDVI(NDVI == -5000) = NaN;
    NDVI = NDVI/10000; % scaling factor
    flag = cat(3,flag1,flag2);
    NDVI(flag >= 4000) = NaN; %remove snow/cloud flagged pixels
    latitude = ncread(fullFileName1, 'lat');
    longitude = ncread(fullFileName1, 'lon');

    md = sum(isnan(NDVI),3);
    ndvi_mean = nanmean(NDVI,3);

    ndvi_monthmax = max(reshape(NDVI,4320,2160,2,12),3); % max NDVI each month
    ndvi_monthmax(:,:,2:end,:) = [];
    ndvi_mmax = squeeze(ndvi_monthmax); % remove 3rd dimension
%HERE'S WHERE I RUN INTO PROBLEMS:
    NDVI_monthmax(:,:,12) = ndvi_mmax;

    %THIS WORKS FINE:
    NDVI_mean(:,:,i) = ndvi_mean;
    MD(:,:,i) = md;
    
end

Answer 1

[Kevin Holly]

Assuming you have 68 files that are distinguished based on the year and the above is only looking at 33 of the files/years.

3D - 4320x2160x(12*68)

NDVI_monthmax(:,:,(i-1)*12:(i-1)*12+12) = ndvi_mmax;

or 4D - 4320x2160x12x68

NDVI_monthmax(:,:,:,i) = ndvi_mmax;

[Kevin Holly]

Or if you just want to append:

NDVI_monthmax = [NDVI_monthmax; ndvi_mmax];

Be sure to write the following command before your for loop:

NDVI_monthmax = [];

[Elin Jacobs]

Works great, thank you!