issues: 857301324

This data as json

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
857301324 MDU6SXNzdWU4NTczMDEzMjQ= 5151 DataArray.mean() emits warning with Dask, not NumPy 1312546 closed 0     3 2021-04-13T20:34:56Z 2021-09-15T16:41:43Z 2021-09-15T16:41:43Z MEMBER      

What happened:

When calling DataArray.mean on an all-NaN dataset, a warning is emitted if and only if a Dask array is used.

What you expected to happen:

Identical behavior between the two, probably no warning .

Minimal Complete Verifiable Example:

```python In [7]: import xarray as xr

In [8]: import numpy as np

In [9]: import dask.array as da

In [10]: import xarray as xr

In [11]: a = xr.DataArray(da.from_array(np.full((10, 10), np.nan)))

In [12]: a.mean(dim="dim_0").compute() /home/taugspurger/miniconda3/envs/tmp-adlfs/lib/python3.8/site-packages/dask/array/numpy_compat.py:39: RuntimeWarning: invalid value encountered in true_divide x = np.divide(x1, x2, out) Out[12]: <xarray.DataArray 'array-395d894c4e4d4ca165a189736da1f52d' (dim_1: 10)> array([nan, nan, nan, nan, nan, nan, nan, nan, nan, nan]) Dimensions without coordinates: dim_1

In [13]: a.compute().mean(dim="dim_0") Out[13]: <xarray.DataArray 'array-395d894c4e4d4ca165a189736da1f52d' (dim_1: 10)> array([nan, nan, nan, nan, nan, nan, nan, nan, nan, nan]) Dimensions without coordinates: dim_1 ```

Anything else we need to know?:

I haven't looked closely at why this is happening (I couldn't immediately find where .mean is reduced). I know that Dask has had some issues in the past where NumPy warnings filters are set during graph construction time, but aren't set when the graph is actually computed.

Environment:

``` INSTALLED VERSIONS ------------------ commit: None python: 3.8.8 | packaged by conda-forge | (default, Feb 20 2021, 16:22:27) [GCC 9.3.0] python-bits: 64 OS: Linux OS-release: 5.4.72-microsoft-standard-WSL2 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: C.UTF-8 LOCALE: en_US.UTF-8 libhdf5: None libnetcdf: None xarray: 0.17.0 pandas: 1.2.4 numpy: 1.20.2 scipy: None netCDF4: None pydap: None h5netcdf: None h5py: None Nio: None zarr: 2.7.0 cftime: None nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2021.04.0 distributed: 2021.04.0 matplotlib: None cartopy: None seaborn: None numbagg: None pint: None setuptools: 52.0.0.post20210125 pip: 21.0.1 conda: None pytest: None IPython: 7.22.0 sphinx: None ``` 
{
    "url": "https://api.github.com/repos/pydata/xarray/issues/5151/reactions",
    "total_count": 0,
    "+1": 0,
    "-1": 0,
    "laugh": 0,
    "hooray": 0,
    "confused": 0,
    "heart": 0,
    "rocket": 0,
    "eyes": 0
}
   completed 13221727 issue

Links from other tables