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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
1831975171 I_kwDOAMm_X85tMbkD 8039 Update assign_coords with a MultiIndex to match new Coordinates API aulemahal 20629530 closed 0     11 2023-08-01T20:22:41Z 2023-08-29T14:23:30Z 2023-08-29T14:23:30Z CONTRIBUTOR      

What is your issue?

A pattern we used in xclim (and elsewhere) seems to be broken on the master.

See MWE: ```python3 import pandas as pd import xarray as xr

da = xr.DataArray([1] * 730, coords={"time": xr.date_range('1900-01-01', periods=730, freq='D', calendar='noleap')}) mulind = pd.MultiIndex.from_arrays((da.time.dt.year.values, da.time.dt.dayofyear.values), names=('year', 'doy'))

Override previous time axis with new MultiIndex

da.assign_coords(time=mulind).unstack('time') ```

Now this works ok with both the current master and the latest release. However, if we chunk da, the last line now fails: python da.chunk(time=50).assign_coords(time=mulind).unstack('time') On the master, this gives: ValueError: unmatched keys found in indexes and variables: {'year', 'doy'}

Full traceback:

--------------------------------------------------------------------------- ValueError Traceback (most recent call last) Cell In[44], line 1 ----> 1 da.chunk(time=50).assign_coords(time=mulind).unstack("time") File ~/Projets/xarray/xarray/core/dataarray.py:2868, in DataArray.unstack(self, dim, fill_value, sparse) 2808 def unstack( 2809 self, 2810 dim: Dims = None, 2811 fill_value: Any = dtypes.NA, 2812 sparse: bool = False, 2813 ) -> DataArray: 2814 """ 2815 Unstack existing dimensions corresponding to MultiIndexes into 2816 multiple new dimensions. (...) 2866 DataArray.stack 2867 """ -> 2868 ds = self._to_temp_dataset().unstack(dim, fill_value, sparse) 2869 return self._from_temp_dataset(ds) File ~/Projets/xarray/xarray/core/dataset.py:5481, in Dataset.unstack(self, dim, fill_value, sparse) 5479 for d in dims: 5480 if needs_full_reindex: -> 5481 result = result._unstack_full_reindex( 5482 d, stacked_indexes[d], fill_value, sparse 5483 ) 5484 else: 5485 result = result._unstack_once(d, stacked_indexes[d], fill_value, sparse) File ~/Projets/xarray/xarray/core/dataset.py:5365, in Dataset._unstack_full_reindex(self, dim, index_and_vars, fill_value, sparse) 5362 else: 5363 # TODO: we may depreciate implicit re-indexing with a pandas.MultiIndex 5364 xr_full_idx = PandasMultiIndex(full_idx, dim) -> 5365 indexers = Indexes( 5366 {k: xr_full_idx for k in index_vars}, 5367 xr_full_idx.create_variables(index_vars), 5368 ) 5369 obj = self._reindex( 5370 indexers, copy=False, fill_value=fill_value, sparse=sparse 5371 ) 5373 for name, var in obj.variables.items(): File ~/Projets/xarray/xarray/core/indexes.py:1435, in Indexes.__init__(self, indexes, variables, index_type) 1433 unmatched_keys = set(indexes) ^ set(variables) 1434 if unmatched_keys: -> 1435 raise ValueError( 1436 f"unmatched keys found in indexes and variables: {unmatched_keys}" 1437 ) 1439 if any(not isinstance(idx, index_type) for idx in indexes.values()): 1440 index_type_str = f"{index_type.__module__}.{index_type.__name__}" ValueError: unmatched keys found in indexes and variables: {'year', 'doy'}

This seems related to PR #7368.

The reason for the title of this issue is that in both versions, I now realize the da.assign_coords(time=mulind) prints as: <xarray.DataArray (time: 730)> dask.array<xarray-<this-array>, shape=(730,), dtype=int64, chunksize=(50,), chunktype=numpy.ndarray> Coordinates: * time (time) object MultiIndex Something's fishy, because the two "sub" indexes are not showing.

And indeed, with the current master, I can get this to work by doing (again changing the last line): python da2 = xr.DataArray(da.data, coords=xr.Coordinates.from_pandas_multiindex(mulind, 'time')) da2.chunk(time=50).unstack('time') But it seems a bit odd to me that we need to reconstruct the DataArray to replace its coordinate with a "MultiIndex" one.

Thus, my questions are:

  1. How does one properly override a coordinate by a MultiIndex ? Is there a way to use assign_coords ? If not, then this issue would become a feature request.
  2. Is this a regression ? Or was I just "lucky" before ?
 
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