issue_comments: 790716187

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https://github.com/pydata/xarray/pull/4979#issuecomment-790716187 https://api.github.com/repos/pydata/xarray/issues/4979 790716187 MDEyOklzc3VlQ29tbWVudDc5MDcxNjE4Nw== 4160723 2021-03-04T15:49:51Z 2021-03-04T15:51:53Z MEMBER

Are the CRSIndex and XgcmIndex examples really independent of any coordinate in the DataArray/Dataset? Looks like in #2996 a CRSIndex could be bound to x and y coordinates and a XgcmIndex could be bound to x, y, x_c, y_c, face, etc. coordinates?

@rabernat @jbusecke (xgcm) @snowman2 @fmaussion @djhoese (crs) it would be interesting to have your thoughts here.

What would be the pros and cons of:

  • Refactoring xgcm.Grid into a XgcmGridIndex? The index would typically be assigned to the Dataset coordinates that are also specified in the coords argument of xgcm.Grid and all other arguments (except the Dataset itself) would become index options. xgcm.Grid methods would then be accessible via Dataset accessor(s) (or eventually just replaced by xarray's corresponding methods).

  • Refactoring a crs attribute (either a "public" Dataset/DataArray attribute or hidden behind an accessor) into some CRSIndex that would typically be assigned to x/y or lat/lon coordinates?

A major advantage is that using a custom index, there's no need to encapsulate a Dataset/DataArray into a higher level structure (e.g., xgcm.Grid) and there would be more control on how it is propagated from one xarray object to another compared to an attribute or via a "stateful" accessor (e.g., crs). Another advantage is that Xarray selection and/or alignment can be customized. But that can be also a downside: unless we allow multiple indexes per coordinate, such XgcmGridIndex and CRSIndex would then have the responsibility of handling selection and alignment for all their corresponding coordinates. That may not be a big deal, though: XgcmGridIndex and CRSIndex could simply encapsulate pandas.Index instances for all (or a subset) of their coordinates.

Are there any other challenges and/or opportunities? (sorry, it has probably been already discussed elsewhere. There's too many places to look for :-) ).

 
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