Add array to NetCDF file as variable

I have a NetCDF file and I'm trying to convert some of the variables into different units. So I extracted the relevant variable (NH4 concentration) and used arrayfun to convert every element in the array to the desired units.

ammdata = ncread('out1.nc','NH4'); % comes out as a 4-D single (lat, long, depth, time)
ammdata2 = arrayfun(@molar,ammdata); % also a 4-D single

function y = molar(x)
    y = x/(14.0067/18.039)*(1/10^3)/(18.039/10^3);
end

Now I need to add the new variable (ammdata2) back to the original NetCDF file as a new variable. I can find documentation online for how to create a new variable, but not how to populate it with an existing multidimentional array.

I currently have the R2021a prerelease installed, not sure if that's relevant.

Answer 1

[KSSV]

Check the demo:

% nc filename to be written
file = 'myfile.nc' ;
delete(file) ;
%% Write lon and lat variables
% Get data
lon = 1:10 ;
lat = 1:10 ;
nx = length(lon) ;
nccreate(file,'lon','Dimensions',{'lon',1,nx},'DeflateLevel',7) ;
ncwrite(file,'lon',lon) ;  
ny = length(lat) ;
nccreate(file,'lat','Dimensions',{'lat',1,ny},'DeflateLevel',7) ;
ncwrite(file,'lat',lat) ;  

nccreate(file,'z','Dimensions',{'lon','lat'},'DeflateLevel',7) ;
data = rand(10) ; 
ncwrite(file,'z',data,[1,1]) ;  
%% Modify and write the variable
lon = ncread(file,'lon') ; 
lat = ncread(file,'lat') ; 
lon_km = deg2km(lon) ;
lat_km = deg2km(lat) ;
% Write variable 
nccreate(file,'lon_kms','Dimensions',{'lon_kms',1,nx},'DeflateLevel',7) ;
ncwrite(file,'lon_kms',lon_km) ;  
nccreate(file,'lat_kms','Dimensions',{'lat_kms',1,ny},'DeflateLevel',7) ;
ncwrite(file,'lat_kms',lat_km) ;