issues: 344631360

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
344631360 MDU6SXNzdWUzNDQ2MzEzNjA= 2315 Behavior of filter_by_attrs() does not match netCDF4.Dataset.get_variables_by_attributes 868027 closed 0     8 2018-07-25T22:35:14Z 2018-08-28T01:21:20Z 2018-08-28T01:21:20Z CONTRIBUTOR      

When using the filter_by_attrs() method of a Dataset it was returning more matches than I expected. The returned match set appears to be the logical OR of all the key=value pairs passed into the method. This does not match the behavior of the netCDF4.Dataset.get_variables_by_attributes which returns the logical AND of all the key=value pairs passed into it. I couldn't tell from the documentation if this was the intended behavior.

Minimal Example

python import xarray as xr example_dataset = xr.Dataset({ "var1": xr.DataArray([], attrs={"standard_name": "example1", "priority": 0}), "var2": xr.DataArray([], attrs={"standard_name": "example2"}) }) example_dataset.filter_by_attrs(standard_name="example2", priority=0)

Example Output

python <xarray.Dataset> Dimensions: (dim_0: 0) Dimensions without coordinates: dim_0 Data variables: var1 (dim_0) float64 var2 (dim_0) float64

Expected Output

python <xarray.Dataset> Dimensions: () Data variables: *empty*

Alternatively, chaining calls to filter_by_attrs will result in the expected behavior: ```python import xarray as xr example_dataset = xr.Dataset({ "var1": xr.DataArray([], attrs={"standard_name": "example1", "priority": 0}), "var2": xr.DataArray([], attrs={"standard_name": "example2"}) }) example_dataset.filter_by_attrs(standard_name="example2").filter_by_attrs(priority=0)

<xarray.Dataset> Dimensions: () Data variables: empty ```

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.7.0.final.0 python-bits: 64 OS: Darwin OS-release: 17.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 xarray: 0.10.8 pandas: 0.23.3 numpy: 1.14.5 scipy: 1.1.0 netCDF4: 1.4.0 h5netcdf: None h5py: None Nio: None zarr: None bottleneck: 1.2.1 cyordereddict: None dask: 0.18.2 distributed: 1.22.0 matplotlib: 2.2.2 cartopy: 0.16.0 seaborn: None setuptools: 39.0.1 pip: 10.0.1 conda: None pytest: 3.6.3 IPython: 6.4.0 sphinx: None 
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