issue_comments: 916974087

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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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