issue_comments: 1249601076

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https://github.com/pydata/xarray/issues/7045#issuecomment-1249601076 https://api.github.com/repos/pydata/xarray/issues/7045 1249601076 IC_kwDOAMm_X85Ke2Y0 1217238 2022-09-16T17:16:52Z 2022-09-16T17:18:38Z MEMBER

IMO we could first align (hah) these choices to be the same:

the exact mode of automatic alignment (outer vs inner vs left join) depends on the specific operation.

The problem is that user expectations are actually rather different for different options:

  • With data movement operations like xarray.merge, you expect to keep around all existing data -- so you want an outer join.
  • With inplace operations that modify an existing Dataset, e.g., by adding new variables, you don't expect the existing coordinates to change -- so you want a left join.
  • With computate based operations (like arithmatic), you don't have an expectation that all existing data is unmodified, so keeping around a bunch of NaN values felt very wasteful -- hence the inner join.

What do you think of making the default FloatIndex use a reasonable (hard to define!) rtol for comparisons?

This would definitely be a step forward! However, it's a tricky nut to crack. We would both need a heuristic for defining rtol (some fraction of coordinate spacing?) and a method for deciding what the resulting coordinates should be (use values from the first object?).

Even then, automatic alignment is often problematic, e.g., imagine cases where a coordinate is defined in separate units.

 
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