BUG: reducing shapely ufunc failing when called on a GeoSeries

[jorisvandenbossche]

Not necessarily an issue in the geopandas code itself, but just opening it here for now to track it somewhere. I ran into this in geopandas/dask-geopandas#268

Calling shapely.geometrycollections on a GeometryArray works fine (it returns a single shapely GeometryCollection geometry object), but calling the same on the equivalent GeoSeries fails:

In [2]: import geopandas

In [3]: arr = geopandas.points_from_xy([0, 1, 2], [1,2,3])

In [4]: arr
Out[4]: 
<GeometryArray>
[<POINT (0 1)>, <POINT (1 2)>, <POINT (2 3)>]
Length: 3, dtype: geometry

In [5]: import shapely

In [6]: shapely.geometrycollections(arr)
Out[6]: <GEOMETRYCOLLECTION (POINT (0 1), POINT (1 2), POINT (2 3))>

In [7]: shapely.geometrycollections(geopandas.GeoSeries(arr))
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[7], line 1
----> 1 shapely.geometrycollections(geopandas.GeoSeries(arr))

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/shapely/decorators.py:77, in multithreading_enabled.<locals>.wrapped(*args, **kwargs)
     75     for arr in array_args:
     76         arr.flags.writeable = False
---> 77     return func(*args, **kwargs)
     78 finally:
     79     for arr, old_flag in zip(array_args, old_flags):

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/shapely/creation.py:460, in geometrycollections(geometries, indices, out, **kwargs)
    458 typ = GeometryType.GEOMETRYCOLLECTION
    459 if indices is None:
--> 460     return lib.create_collection(geometries, typ, out=out, **kwargs)
    461 else:
    462     return collections_1d(geometries, indices, typ, out=out)

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/pandas/core/generic.py:2168, in NDFrame.__array_ufunc__(self, ufunc, method, *inputs, **kwargs)
   2164 @final
   2165 def __array_ufunc__(
   2166     self, ufunc: np.ufunc, method: str, *inputs: Any, **kwargs: Any
   2167 ):
-> 2168     return arraylike.array_ufunc(self, ufunc, method, *inputs, **kwargs)

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/pandas/core/arraylike.py:414, in array_ufunc(self, ufunc, method, *inputs, **kwargs)
    411         result = default_array_ufunc(inputs[0], ufunc, method, *inputs, **kwargs)
    412         # e.g. np.negative (only one reached), with "where" and "out" in kwargs
--> 414 result = reconstruct(result)
    415 return result

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/pandas/core/arraylike.py:343, in array_ufunc.<locals>.reconstruct(result)
    339 if ufunc.nout > 1:
    340     # np.modf, np.frexp, np.divmod
    341     return tuple(_reconstruct(x) for x in result)
--> 343 return _reconstruct(result)

File ~/conda/envs/geo-dev/lib/python3.11/site-packages/pandas/core/arraylike.py:349, in array_ufunc.<locals>._reconstruct(result)
    346 if lib.is_scalar(result):
    347     return result
--> 349 if result.ndim != self.ndim:
    350     if method == "outer":
    351         raise NotImplementedError

AttributeError: 'GeometryCollection' object has no attribute 'ndim'