issues: 1865494976

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1865494976 PR_kwDOAMm_X85Ytlq0 8111 Alignment: allow flexible index coordinate order 4160723 open 0     3 2023-08-24T16:18:49Z 2023-09-28T15:58:38Z   MEMBER   0 pydata/xarray/pulls/8111
  • [x] Closes #7002
  • [x] Tests added
  • [x] User visible changes (including notable bug fixes) are documented in whats-new.rst

This PR relaxes some of the rules used in alignment for finding the indexes to compare or join together. Those indexes must still be of the same type and must relate to the same set of coordinates (and dimensions), but the order of coordinates is now ignored.

It is up to the index to implement the equal / join logic if it needs to care about that order.

Regarding pandas.MultiIndex, it seems that the level names are ignored when comparing indexes:

```python midx = pd.MultiIndex.from_product([["a", "b"], [0, 1]], names=("one", "two"))) midx2 = pd.MultiIndex.from_product([["a", "b"], [0, 1]], names=("two", "one"))

midx.equals(midx2) # True ```

However, in Xarray the names of the multi-index levels (and their order) matter since each level has its own xarray coordinate. In this PR, PandasMultiIndex.equals() and PandasMultiIndex.join() thus check that the level names match. 

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