Creating a NetCDF (.nc) file with variables that contain a different dimension

I am in the process of creating a code that converts various global grids taken along a time series (a few months) into a NetCDF (.nc) file (i.e. lon x lat x time). I have understood the general process of netcdf. Unfortunately I can't manage to save the grids with different sizes in different variables. If it is possible at all, how does this work?

Below is a code example that throws an error because it does not contain the same dimension:

grid1 = ones(180 , 360 , 5); % e.g. 180°x360° grid along 5 months
grid2 = ones(180 , 360 , 8); % e.g. 180°x360° grid along 8 months
grid3 = ones( 90 , 180 , 5); % e.g.  90°x180° grid along 5 months

nccreate("myfile.nc","grid1","Dimensions", {"lat",180,"lon",360,"t",5},"Format","classic");
ncwrite("myfile.nc","grid1",grid1);


nccreate("myfile.nc","grid2","Dimensions", {"lat",180,"lon",360,"t",8},"Format","classic");

Error using internal.matlab.imagesci.nc/createDimension (line 1174)
Cannot create dimension 't' of length 8. '/' already defines a fixed length dimension of the same name with length 5. Existing dimensions cannot be resized.

Error in internal.matlab.imagesci.nc/createDimensions (line 289)
this.createDimension(defgid, ...

Error in internal.matlab.imagesci.nc/createVariable (line 422)
this.createDimensions(groupName, dimensions);

Error in nccreate (line 182)
ncObj.createVariable(varName, varargin{:})

ncwrite("myfile.nc","grid2",grid2);


nccreate("myfile.nc","grid3","Dimensions", {"lat", 90,"lon",180,"t",5},"Format","classic");
ncwrite("myfile.nc","grid3",grid3);

Is it somehow possible not to define the dimension globally for all variables or is there any other possibility?

Answer 1

[Ayush Modi]

Hi Simon,

You can define different dimension for each variable while creating the variables using "nccreate" function. Here is the modified code to achieve the same:

nccreate("myfile.nc", "grid1", "Dimensions", {"lat1", 180, "lon1", 360, "t1", 5}, "Format", "classic");

nccreate("myfile.nc", "grid2", "Dimensions", {"lat2", 180, "lon2", 360, "t2", 8}, "Format", "classic");

nccreate("myfile.nc", "grid3", "Dimensions", {"lat3", 90, "lon3", 180, "t3", 5}, "Format", "classic");

% Note, Dimension argument is added in each "nccreate" statement to define
% different dimensions for each variable.

Please refer to the following MathWorks documentation for more information on "Dimension" argument in "nccreate" function:

https://www.mathworks.com/help/matlab/ref/nccreate.html#:~:text=Dimensions%20%E2%80%94%20Dimensions%20of%20variable

[Simon Schiller]

Yes, that works very well in my case. Thank you for your help, that solves my problem!