Xarray: Using `DataArray.where()` with a DataArray as the condition drops the name

[jacklovell]

Code Sample, a copy-pastable example if possible

Create a boolean DataArray to use as a mask for another DataArray, with the same coordinates:

da_1 = xr.DataArray(np.array([0.861185, 0.301491, 0.642744, 0.773298, 0.786516, 0.011693, 0.659326, 0.07877 , 0.108488, 0.747863]), coords=[('coord1', np.arange(10))], name='da1')
da_2 = xr.DataArray(np.array([0.116959, 0.955742, 0.121562, 0.635573, 0.304895, 0.064529, 0.042461, 0.41751 , 0.607457, 0.110104]), coords=[('coord1', np.arange(10))], name='da2')
da_3 = np.rint(da_2).astype('bool')
print(da_1)
<xarray.DataArray 'da1' (coord1: 10)>
array([0.861185, 0.301491, 0.642744, 0.773298, 0.786516, 0.011693, 0.659326,
       0.07877 , 0.108488, 0.747863])
Coordinates:
  * coord1   (coord1) int64 0 1 2 3 4 5 6 7 8 9
print(da_1.where(da_3))
<xarray.DataArray (coord1: 10)>
array([     nan, 0.301491,      nan, 0.773298,      nan,      nan,      nan,
            nan, 0.108488,      nan])
Coordinates:
  * coord1   (coord1) int64 0 1 2 3 4 5 6 7 8 9

Problem description

When using a DataArray (da_3 in the example) as the condition in the where() method of another DataArray (da_1), the name of the DataArray being masked (da_1) is dropped.

Expected Output

The name should be retained.

print(da_1.where(da_3))
<xarray.DataArray 'da_1` (coord1: 10)>
array([     nan, 0.301491,      nan, 0.773298,      nan,      nan,      nan,
            nan, 0.108488,      nan])
Coordinates:
  * coord1   (coord1) int64 0 1 2 3 4 5 6 7 8 9

Output of xr.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Linux
OS-release: 4.13.0-38-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8

xarray: 0.10.3
pandas: 0.22.0
numpy: 1.14.3
scipy: 1.1.0
netCDF4: 1.3.2
h5netcdf: None
h5py: 2.7.1
Nio: None
zarr: None
bottleneck: 1.2.1
cyordereddict: None
dask: 0.17.4
distributed: 1.21.8
matplotlib: 2.2.2
cartopy: None
seaborn: 0.8.1
setuptools: 39.1.0
pip: 10.0.1
conda: 4.5.2
pytest: 3.5.1
IPython: 6.4.0
sphinx: 1.7.4

[shoyer]

Indeed, we should have some sort of logic to indicate that the name from the original DataArray should be preserved.

Under the hood, DataArray.where uses xarray.apply_ufunc. So maybe this should be coupled with keep_attrs=True in xarray.apply_ufunc()?

[jacklovell]

Yes, I think it makes sense to couple it with keep_attrs=True. One could question whether the name should be considered separate to the attributes (and therefore have an additional keyword argument for keeping the name), but I think in most cases it makes sense to keep the name if you're already keeping the attributes, and to drop the name if you're dropping the attributes.

[stale[bot]]

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If this issue remains relevant, please comment here or remove the stale label; otherwise it will be marked as closed automatically

[jacklovell]

This bug appears to have been fixed, as of Xarray 0.15.0.