Add `fill` to `.sel` for missing values. about xarray HOT 5 OPEN

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IIUC we call this reindex: https://docs.xarray.dev/en/stable/generated/xarray.Dataset.reindex.html

Do you think the docs for sel can be improved to point this out?

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reindex is close to the behavior we want, but mandates that the indexer has the same dims as the target.
In this operation, we're indexing along a single dim with a multi-dimensional coord.
So we expect the selection + fill to result in a differently-dimensioned structure.

I've put a gist up at: https://gist.github.com/asford/b10a9f62b3657be7a122b3411e90ba2a

I may not be invoking this correctly, happy to further guidance.

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Clarified in description, perhaps an adaptation of reindex rather than sel?
The naïve dat.reindex(letter=query.stack(letter=query.dims)) breaks because reindex ends up replacing the coord index (which we want to preserve) with the indexing values.

from xarray.

perhaps an adaptation of reindex rather than sel?

I think this would make more sense indeed. Similarly to advanced indexing, advanced reindexing might perhaps be done by passing xarray Variable or DataArray objects as indexer mapping values to .reindex() and checking their dimensions. Not sure about the amount of internal refactoring this would require, though.

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