How to know if a sliced xarray Dataset/DataArray is empty?

Question

I am applying slicing and aggregation operations over Netcdf files in Python language. One of the solutions for working with this kind of file is to use the Xarray library.

I am still new to the library functionalities, so I would like to know whether Xarray objects possess some method to check if a sliced DataSet/DataArray is empty or not, just like Pandas has (in the case of pandas, one can check if the dataframe/series is empty through the 'empty' method).

The only solution I found was to always convert the Xarray Dataset/DataArray into a pandas Dataframe/Series, to then check if it is empty or not.

Here is code snippet as example:

import xarray as xr

path = 'my_path_to_my_netcdf_file.nc'

Xarray_DataArray = xr.open_dataset(path)

print(Xarray_DataArray)

# this returns something like:

 #     Dimensions:      (lat: 600, lon: 672, time: 37)
 #     Coordinates:
 #     * lat          (lat) float32 -3.9791672 -3.9375012 ... 20.9375 20.979166
 #     * lon          (lon) float32 -60.979168 -60.9375 ... -33.0625 -33.020832
 #     * time         (time) datetime64[ns] 2010-05-19 2010-05-20 ... 2010-06-24
 #     Data variables:
 #       variable_name  (time, lat, lon) float32 dask.array<shape=(37, 600, 672), 
 #         chunksize=(37, 600, 672)>

 # I normally use the 'sel' method to slice the xarray object, like below:

Sliced_Xarray_DataArray = Xarray_DataArray.sel({'lat':slice(-10, -9),
                                                'lon':slice(-170, -169)                  
                                                })


 # but since, Xarray does not possess a proper way to check the slice, I usually have to do the following:

 if Sliced_Xarray_DataArray.to_dataframe().empty():
    print('is empty. Nothing to aggregate')

 else:
    Aggregated_value =  Aggregation_function(Sliced_Xarray_DataArray)

    print('continuing with the analysis')


 #    ... continue

I would appreciate any suggestions.

I thank you for your time, and I hope hearing from you soon.

Sincerely yours,

Philipe R. Leal

Answer 1

You can check if the size of the variables in the resulting slice is 0 easily enough:

print(Sliced_Xarray_DataArray.time.size)
if Sliced_Xarray_DataArray.time.size == 0:
    print('is empty. Nothing to aggregate')
else:
    print('not empty. Go aggregate')

Any of your coordinate variables as well us other variables will be accessible as attributes in your Sliced_Xarray_DataArray so in your example you could check the size of lat, lon or time.