html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/4825#issuecomment-916974087,https://api.github.com/repos/pydata/xarray/issues/4825,916974087,IC_kwDOAMm_X842p-oH,4160723,2021-09-10T15:04:14Z,2021-09-10T15:04:14Z,MEMBER,"I think that the explicit index refactoring would be an opportunity to clarify things a bit. With no concept of a dimension coordinate/ implicit index, *ideally* we could have the following behavior with a clear distinction between dimensions/coordinates and indexes, following more closely the ""explicit is better than implicit"" principle:

- `set_index` / `reset_index` would only affect the indexes without implicitly renaming any coordinate or dimension.
  - actually, setting a new index for a given dimension doesn't make much sense anymore with the new data model. Setting a new index for a given set of variables and/or coordinates makes more sense
  - trying to set an index from non-existing data variables or coordinates would raise a `KeyError`
  - `.reset_index(""x"")` would not rename the `x` coordinate to `x_`
  - `.set_index(x=""b"")` (where `x` is a dimension without index/coordinate and `b` is a variable with dimension `x`) would be replaced by a more explicit `set_index(""b"").rename({""b"": ""x""})`. Renaming `b` to `x` wouldn't even be necessary if we want to use the `b` coordinate as an index. 
  
- `rename_*` would only affect the name of coordinates or dimensions (or the name of the DataArray) without implicitly adding or removing any index.
  - `.set_coords(""b"").rename({""b"": ""x""})` in the example above would not implictly create an index for the ""x"" coordinate 

- `swap_dims` would only affect the existing dimension names without implicitly adding or removing any index and without renaming any coordinate.

This would be in an ideal world, though. More practically, I don't know how we could make a smooth transition.

> There's also rename_dims, but only on a Dataset! There's a TODO to deprecate swap_dims in favor of that. Though I'm not sure that's right — swap_dims changes the dim values for another variable's, but rename_dims just changes the name?

`swap_dims` used as a workaround for switching from one to another coordinate as index on a dimension will no longer be needed after the explicit indexes refactoring. Should we eventually depreciate it, then?

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