issues: 1830038411

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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
1830038411 PR_kwDOAMm_X85W2FcN 8034 sort when encoding coordinates for deterministic outputs 3383837 closed 0     0 2023-07-31T21:16:31Z 2023-08-03T16:27:28Z 2023-08-03T16:27:27Z CONTRIBUTOR   0 pydata/xarray/pulls/8034
  • [x] Closes #8026
  • [x] Tests added
  • [x] User visible changes (including notable bug fixes) are documented in whats-new.rst
  • ~~[ ] New functions/methods are listed in api.rst~~

The PR changes conventions._encode_coordinates to add sorted during the creation of "coordinates" strings de novo. It does not touch user-specified coordinates attributes or encodings.

The PR adds a test, but also changes two pre-existing tests that allowed for non-deterministic ordering of the coordinates string.

In reviewing the netCDF data model and CF convenstions, I confirmed that there is no requirement on the ordering of names in the coordinates attribute. I also learned that the global coordinates attribute created by XArray for non-dimension coordinates that are not associated with a variable is not compliant with CF conventions, as was discussed in 2014. In 2021, CF-Conventions 1.9 added "Domain Variables", which appear to provide a CF compliant way to handle this situation. I will likely open an enhancement issue to weigh making that change.

 
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