我在Mac OS X El Capitan 10.11.6上使用Xarray版本0.8.0，Python 3.5.1。
以下代码按预期工作。
id_data_array = xarray.DataArray([280, 306, 280], coords={"index": range(3)})
random = numpy.random.rand(3)
score_data_array = xarray.DataArray(random, coords={"index": range(3)})
score_dataset = xarray.Dataset({"id": id_data_array, "score": score_data_array})
print(score_dataset)
print("======")
print(score_dataset.groupby("id").count())
输出：
<xarray.Dataset>
Dimensions: (index: 3)
Coordinates:
* index (index) int64 0 1 2
Data variables:
id (index) int64 280 306 280
score (index) float64 0.8358 0.7536 0.9495
======
<xarray.Dataset>
Dimensions: (id: 2)
Coordinates:
* id (id) int64 280 306
Data variables:
score (id) int64 2 1
In [ ]:
但是，如果我只改变一件小事，为了使id_data_array的元素全部不同，则会出现错误。
代码：
id_data_array = xarray.DataArray([280, 306, 120], coords={"index": range(3)})
random = numpy.random.rand(3)
score_data_array = xarray.DataArray(random, coords={"index": range(3)})
score_dataset = xarray.Dataset({"id": id_data_array, "score": score_data_array})
print(score_dataset)
print("======")
print(score_dataset.groupby("id").count())
输出：
<xarray.Dataset>
Dimensions: (index: 3)
Coordinates:
* index (index) int64 0 1 2
Data variables:
id (index) int64 280 306 120
score (index) float64 0.1353 0.0437 0.1687
======
---------------------------------------------------------------------------
InvalidIndexError Traceback (most recent call last)
<ipython-input-92-cc412270ba2e> in <module>()
5 print(score_dataset)
6 print("======")
----> 7 print(score_dataset.groupby("id").count())
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/common.py in wrapped_func(self, dim, keep_attrs, **kwargs)
44 return self.reduce(func, dim, keep_attrs,
45 numeric_only=numeric_only, allow_lazy=True,
---> 46 **kwargs)
47 return wrapped_func
48
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/groupby.py in reduce(self, func, dim, keep_attrs, **kwargs)
605 def reduce_dataset(ds):
606 return ds.reduce(func, dim, keep_attrs, **kwargs)
--> 607 return self.apply(reduce_dataset)
608
609 def assign(self, **kwargs):
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/groupby.py in apply(self, func, **kwargs)
562 kwargs.pop('shortcut', None) # ignore shortcut if set (for now)
563 applied = (func(ds, **kwargs) for ds in self._iter_grouped())
--> 564 combined = self._concat(applied)
565 result = self._maybe_restore_empty_groups(combined)
566 return result
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/groupby.py in _concat(self, applied)
570 concat_dim, positions = self._infer_concat_args(applied_example)
571
--> 572 combined = concat(applied, concat_dim)
573 reordered = _maybe_reorder(combined, concat_dim, positions)
574 return reordered
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/combine.py in concat(objs, dim, data_vars, coords, compat, positions, indexers, mode, concat_over)
114 raise TypeError('can only concatenate xarray Dataset and DataArray '
115 'objects, got %s' % type(first_obj))
--> 116 return f(objs, dim, data_vars, coords, compat, positions)
117
118
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/combine.py in _dataset_concat(datasets, dim, data_vars, coords, compat, positions)
276 if coord is not None:
277 # add concat dimension last to ensure that its in the final Dataset
--> 278 result[coord.name] = coord
279
280 return result
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/dataset.py in __setitem__(self, key, value)
536 raise NotImplementedError('cannot yet use a dictionary as a key '
537 'to set Dataset values')
--> 538 self.update({key: value})
539
540 def __delitem__(self, key):
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/dataset.py in update(self, other, inplace)
1434 dataset.
1435 """
-> 1436 variables, coord_names, dims = dataset_update_method(self, other)
1437
1438 return self._replace_vars_and_dims(variables, coord_names, dims,
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/merge.py in dataset_update_method(dataset, other)
490 priority_arg = 1
491 indexes = dataset.indexes
--> 492 return merge_core(objs, priority_arg=priority_arg, indexes=indexes)
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/merge.py in merge_core(objs, compat, join, priority_arg, explicit_coords, indexes)
371
372 coerced = coerce_pandas_values(objs)
--> 373 aligned = deep_align(coerced, join=join, copy=False, indexes=indexes)
374 expanded = expand_variable_dicts(aligned)
375
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/alignment.py in deep_align(list_of_variable_maps, join, copy, indexes)
146 out.append(variables)
147
--> 148 aligned = partial_align(*targets, join=join, copy=copy, indexes=indexes)
149
150 for key, aligned_obj in zip(keys, aligned):
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/alignment.py in partial_align(*objects, **kwargs)
109 valid_indexers = dict((k, v) for k, v in joined_indexes.items()
110 if k in obj.dims)
--> 111 result.append(obj.reindex(copy=copy, **valid_indexers))
112 return tuple(result)
113
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/dataset.py in reindex(self, indexers, method, tolerance, copy, **kw_indexers)
1216
1217 variables = alignment.reindex_variables(
-> 1218 self.variables, self.indexes, indexers, method, tolerance, copy=copy)
1219 return self._replace_vars_and_dims(variables)
1220
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/xarray/core/alignment.py in reindex_variables(variables, indexes, indexers, method, tolerance, copy)
218 target = utils.safe_cast_to_index(indexers[name])
219 indexer = index.get_indexer(target, method=method,
--> 220 **get_indexer_kwargs)
221
222 to_shape[name] = len(target)
/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/pandas/indexes/base.py in get_indexer(self, target, method, limit, tolerance)
2080
2081 if not self.is_unique:
-> 2082 raise InvalidIndexError('Reindexing only valid with uniquely'
2083 ' valued Index objects')
2084
InvalidIndexError: Reindexing only valid with uniquely valued Index objects
对我来说，这似乎是错误的，因为如果这是理想的行为，那将是非常奇怪的。当然，我们应该在我们分组的DataArray的所有元素都不同的情况下包含这种情况吗？
我现在已经卸载并重新安装了Xarray。新的Xarray版本为0.8.1，似乎工作正常。所以它可能确实是Xarray 0.8.0中的一个错误。