How to create a a scalar NetCDF variable (i.e with no dimensions)?

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Jonathan Blythe
Jonathan Blythe 2011-12-9
评论： Mary Jo Brodzik 2023-6-16
I need to define a NetCDF variable with a dimension of size zero. The NetCDF function, netcdf.defVar requires a dimid, but it is not possible to define a dimension of length zero, since assigning zero in netcdf.defDim produces an unlimited dimension. Does matlab have any native functions to support zero length variables?

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Ashish Uthama
Ashish Uthama 2011-12-9
Could you tell us why would you need a dimension of size zero?
Are you trying to create a scalar variable? If so, try [] for the dimid in the call to netcdf.defVar. (You could also try the newer nccreate if you have it.)

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Jonathan Blythe
Jonathan Blythe 2011-12-12
Thank you, this did the trick.
We use 'empty' NetCDF variables to tack ancillary metadata. In this case, the Climate and Forecast conventions specify a variable called Grid Mapping that is one instance of this.
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Mary Jo Brodzik
Mary Jo Brodzik 2023-6-16
I needed to do this same task and it took me a long time to come across this answer. One additional note for others who may also be puzzled: for the CF grid_mapping variable, you only need to define the variable and then add the projection attributes, no need to use 'putVar' to populate it with anything degenerate, e.g.:
varid = netcdf.defVar(ncid, 'crs', 'NC_INT', []);
netcdf.endDef(ncid);
netcdf.putAtt(ncid, varid, 'grid_mapping_name', 'sinusoidal');
% ...then use putAtt for the rest of the 'crs' attributes

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