docs: document sort-order behavior of unstack() for pandas-origin MultiIndex#11363
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emfdavid wants to merge 2 commits into
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docs: document sort-order behavior of unstack() for pandas-origin MultiIndex#11363emfdavid wants to merge 2 commits into
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Still some CICD errors but these don't appear to be related to my changes. |
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Thanks the test failures seem related? |
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Much better after rebase - now just a pixi/numcodecs issue! |
…tiIndex When a DataArray/Dataset is built from a pandas object whose MultiIndex was created by pandas directly (e.g. pd.Series.set_index), pandas stores MultiIndex.levels in sorted order regardless of insertion order. As a result, the coordinates of the new dimensions after unstack() are sorted, not in original insertion order. Add a 'Notes / Sort order' section to DataArray.unstack and Dataset.unstack docstrings explaining this behavior and how to restore a specific order with .sel(). Also add test_unstack_coords_are_sorted to demonstrate the behavior via a pd.Series with a pd.MultiIndex. Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Document unexpected sorting behavior in unstack
This PR changes only Docs and adds a test demonstrating the behavior.
Summary
When a
DataArray/Datasetis built from a pandas object whoseMultiIndexwas created directly by pandas (e.g. viapd.Series.set_indexorpd.MultiIndex.from_arrays), pandas storesMultiIndex.levelsin sorted order regardless of insertion order. As a result, the coordinates of the new dimensions afterunstack()are sorted, not in original insertion order.This is distinct from xarray's own
stack(), which preserves insertion order viafactorize()for non-monotonic inputs.This silent behaviour can cause subtle bugs when user code extracts
.data(a positional numpy array) and labels it with coordinates assumed to be in insertion order.Changes
Notes / Sort ordersection toDataArray.unstackandDataset.unstackdocstrings explaining the behavior and how to restore a specific order with.sel()test_unstack_coords_are_sortedtotest_dataarray.pyto demonstrate the behavior via apd.Serieswith apd.MultiIndex[This PR was opened by Claude on behalf of emfdavid]