save dataset as netCDF and also save attributes in Python (xarray)

Question

I generated new data and save first as dataset (.to_dataset).

U_reg = U_reg.to_dataset(name = 'U')
V_reg = V_reg.to_dataset(name = 'V')
T_reg = T_reg.to_dataset(name = 'T')

Then I created attributes for each variable

U_reg.attrs['long_name'] = 'eastward_wind'
V_reg.attrs['long_name'] = 'northward_wind'
T_reg.attrs['long_name'] = 'Air Temperature'

Then merged the data as :

new_data= xr.merge([U_reg,V_reg,T_reg])

For finally save as a netCDF:

new_data.to_netCDF('new_data.netcdf')

Nevertheless when I open and look at each variable, the attributes are not available.

Is there other way to assign new attributes and have them I the new netCDF generated?

Thanks in advance.

jhamman · Accepted Answer · 2023-06-09 04:11:06Z

In your example, you were adding the long_name attribute to the dataset attributes, rather than the attributes for the individual arrays. If you add the attributes before you convert to a dataset (or directly to the dataset variables), you should get your expected output:

U_reg = xr.DataArray(np.random.random((5, 6, 7)), dims=("lon", "lat", "time"))
V_reg = xr.DataArray(np.random.random((5, 6, 7)), dims=("lon", "lat", "time"))
T_reg = xr.DataArray(np.random.random((5, 6, 7)), dims=("lon", "lat", "time"))

U_reg.attrs['long_name'] = 'eastward_wind'
V_reg.attrs['long_name'] = 'northward_wind'
T_reg.attrs['long_name'] = 'Air Temperature'

ds = xr.Dataset({
    "U": U_reg,
    "V": V_reg,
    "T": T_reg
})

ds.info()

xarray.Dataset {
dimensions:
    lon = 5 ;
    lat = 6 ;
    time = 7 ;

variables:
    float64 U(lon, lat, time) ;
        U:long_name = eastward_wind ;
    float64 V(lon, lat, time) ;
        V:long_name = northward_wind ;
    float64 T(lon, lat, time) ;
        T:long_name = Air Temperature ;

// global attributes:

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