issues: 709503596

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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
709503596 MDU6SXNzdWU3MDk1MDM1OTY= 4465 combine_by_coords could use allclose instead of equal to compare coordinates 10563614 open 0     4 2020-09-26T09:26:05Z 2020-09-26T21:30:35Z   CONTRIBUTOR      

Is your feature request related to a problem? Please describe.

When a coordinate in different dataset / netcdf files has slightly different values, combine_by_coords considers the coordinate are different and attempts a concatenation of the coordinates.

Concretely, I produce netcdf with (lat, lon, time) coordinates, annually. Apparently the lat is not the same in all the files (difference is 1e-14), which I suspect is due to different pyproj version used to produce the lon,lat grid. Reprocessing all the annual netcdf is not an option. When using open_mfdataset on these netcdf, the lat coordinate is concatenated which leads to a MemoryError in my case.

Describe the solution you'd like Two options: - add a coord_tolerance argument to xr.combine_by_coords and use np.allclose to compare the coordinates. In line 69 combine.py the comparison uses strict equality "if not all(index.equals(indexes[0]) for index in indexes[1:]):". This does not break the compatibility because coord_tolerance=0 should be the default.

  • add an argument to explicity list the coordinates to NOT concatenate. I tried to play with the coords argument to solve my problem, but was not succesfull.

Describe alternatives you've considered

  • I certainly could find a workaround for this specific case, but I often had issue with the magic in combine_by_coords, and imho adding more control by the user would be useful in general.

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