html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/1537#issuecomment-326164860,https://api.github.com/repos/pydata/xarray/issues/1537,326164860,MDEyOklzc3VlQ29tbWVudDMyNjE2NDg2MA==,6815844,2017-08-31T01:39:00Z,2017-08-31T01:39:00Z,MEMBER,"Thanks for the investigation.
This is strange.

I raised an issue in https://github.com/numpy/numpy/issues/9633.
As it is clear xarray cannot do anything about it, I close this issue.

","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,253975242
https://github.com/pydata/xarray/issues/1537#issuecomment-326157538,https://api.github.com/repos/pydata/xarray/issues/1537,326157538,MDEyOklzc3VlQ29tbWVudDMyNjE1NzUzOA==,1217238,2017-08-31T00:44:41Z,2017-08-31T00:44:41Z,MEMBER,"OK, here we go:
```
In [25]: class GoodWrappedArray(object):
    ...:     def __init__(self, array):
    ...:         self.array = array
    ...:     def __array__(self, dtype=None):
    ...:         return np.asarray(self.array, dtype)
    ...:     def __getitem__(self, key):
    ...:         return self.array[key]
    ...:     def __len__(self):
    ...:         return len(self.array)
    ...:

In [26]: ind = GoodWrappedArray(np.array([True, False, True]))

In [27]: np.arange(3)[ind]
Out[27]: array([0, 2])

In [28]: class BadWrappedArray(object):
    ...:     def __init__(self, array):
    ...:         self.array = array
    ...:     def __array__(self, dtype=None):
    ...:         return np.asarray(self.array, dtype)
    ...:     def __getitem__(self, key):
    ...:         return BadWrappedArray(self.array[key])
    ...:     def __len__(self):
    ...:         return len(self.array)
    ...:

In [29]: ind = BadWrappedArray(np.array([True, False, True]))

In [30]: np.arange(3)[ind]
Out[32]: array([], shape=(0, 3), dtype=int64)
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,253975242
https://github.com/pydata/xarray/issues/1537#issuecomment-326157080,https://api.github.com/repos/pydata/xarray/issues/1537,326157080,MDEyOklzc3VlQ29tbWVudDMyNjE1NzA4MA==,1217238,2017-08-31T00:41:25Z,2017-08-31T00:41:25Z,MEMBER,"Two more clues:

LazilyIndexedArray suffices to duplicate this issue:
```
In [20]: ind = xr.core.indexing.LazilyIndexedArray(np.array([True, False, True]))

In [21]: np.arange(3)[ind]
Out[21]: array([], shape=(0, 3), dtype=int64)
```

But this simple array wrapper does not:
```
In [17]: class WrappedArray(object):
    ...:     def __init__(self, array):
    ...:         self.array = array
    ...:     def __array__(self, dtype=None):
    ...:         return np.asarray(self.array, dtype)
    ...:     def __getitem__(self, key):
    ...:         return WrappedArray(self.array[key])
    ...:     @property
    ...:     def shape(self):
    ...:         return self.array.shape
    ...:     @property
    ...:     def dtype(self):
    ...:         return self.array.dtype
    ...:

In [18]: ind = WrappedArray(np.array([True, False, True]))

In [19]: np.arange(3)[ind]
Out[19]: array([0, 2])
```","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,253975242
https://github.com/pydata/xarray/issues/1537#issuecomment-326154495,https://api.github.com/repos/pydata/xarray/issues/1537,326154495,MDEyOklzc3VlQ29tbWVudDMyNjE1NDQ5NQ==,6815844,2017-08-31T00:21:53Z,2017-08-31T00:21:53Z,MEMBER,"I will raise an issue in NumPy.
It might better if we could tell which part of our code causes this bug.
(And if we can avoid it within our code, it might be much quicker)
Do you have any idea?

I confirmed
+ indexing by a `Variable` already causes this bug
+ only simple subclassing `common.AbstractArray` and `utils.NdimSizeLenMixin` does not cause this.

I suspect something related to `Variable` interpretation could trigger it.
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,253975242
https://github.com/pydata/xarray/issues/1537#issuecomment-326037970,https://api.github.com/repos/pydata/xarray/issues/1537,326037970,MDEyOklzc3VlQ29tbWVudDMyNjAzNzk3MA==,1217238,2017-08-30T16:01:32Z,2017-08-30T16:01:32Z,MEMBER,"I think this is probably an upstream (numpy) bug. Indexing a NumPy array by an array-like object should be equivalent to casting it to a numpy array, i.e., `array[np.asarray(ind)]`.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,253975242