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
391721237,MDExOlB1bGxSZXF1ZXN0MjM5MTUxMzQ3,2615,"FIX Don't raise a deprecation warning for xarray.ufuncs.{angle,iscomplex}",630936,closed,0,,,2,2018-12-17T13:51:06Z,2018-12-20T18:10:20Z,2018-12-20T18:01:39Z,CONTRIBUTOR,,0,pydata/xarray/pulls/2615,"Closes https://github.com/pydata/xarray/issues/2609

This removes PendingDeprecationWarnings for `xarray.ufuncs.{angle,iscomplex}` which appear to not be proper ufuncs and cannot be just used from numpy for now (as discussed in the parent issue).

Also adds more generic tests that numpy ufuncs do preserve the DataArray dtype.","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/2615/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
391398977,MDU6SXNzdWUzOTEzOTg5Nzc=,2609,Cannot replace xr.ufuncs.angle with np.angle,630936,closed,0,,,2,2018-12-15T18:01:46Z,2018-12-20T18:01:38Z,2018-12-20T18:01:38Z,CONTRIBUTOR,,,,"Currently one gets a deprecation warning when using `xarray.ufuncs.angle` on a DataArray with xarray 0.11 and numpy 1.15, e.g.
```
PendingDeprecationWarning: xarray.ufuncs will be deprecated when xarray no longer supports versions of numpy older than v1.13. Instead, use numpy ufuncs directly.
    X_tr = xr.ufuncs.angle(X)
```

however, `np.angle` still casts the input to `ndarray`, apparently.

#### Code Sample, a copy-pastable example if possible


```python
>>> import xarray as xr
>>> import numpy as np
>>> X = xr.DataArray(np.ones(10))
>>> X
<xarray.DataArray (dim_0: 10)>
array([1., 1., 1., 1., 1., 1., 1., 1., 1., 1.])
Dimensions without coordinates: dim_0
>>> xr.ufuncs.angle(X)  # expected output
<xarray.DataArray (dim_0: 10)>
array([0., 0., 0., 0., 0., 0., 0., 0., 0., 0.])
Dimensions without coordinates: dim_0
>>> np.angle(X)  # actual output
array([0., 0., 0., 0., 0., 0., 0., 0., 0., 0.])
>>> np.__version__
'1.15.4'
>>> xr.__version__
'0.11.0'
>>> np.sin(X)  # other ufuns work
<xarray.DataArray (dim_0: 10)>
array([0.841471, 0.841471, 0.841471, 0.841471, 0.841471, 0.841471, 0.841471,
       0.841471, 0.841471, 0.841471])
Dimensions without coordinates: dim_0
```
#### Problem description

I have not investigated yet why happens in numpy, but opening this issue to indicate that currently I can't really do much about this DeprecationWarning sort of silencing it (unless I'm missing something).

#### Output of ``xr.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.18.8-gentoo
machine: x86_64
processor: Intel(R) Core(TM) i5-6200U CPU @ 2.30GHz
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8

xarray: 0.11.0
pandas: 0.23.4
numpy: 1.15.4
scipy: 1.1.0
netCDF4: None
h5netcdf: 0.6.2
h5py: 2.8.0
Nio: None
zarr: None
cftime: None
PseudonetCDF: None
rasterio: None
iris: None
bottleneck: None
cyordereddict: None
dask: 1.0.0
distributed: None
matplotlib: 3.0.2
cartopy: None
seaborn: None
setuptools: 40.6.2
pip: 18.1
conda: None
pytest: 4.0.1
IPython: None
sphinx: None

</details>
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/2609/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue