issue_comments: 490394601

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https://github.com/pydata/xarray/issues/2946#issuecomment-490394601 https://api.github.com/repos/pydata/xarray/issues/2946 490394601 MDEyOklzc3VlQ29tbWVudDQ5MDM5NDYwMQ== 10809480 2019-05-08T08:18:21Z 2019-05-08T09:01:56Z NONE

fixed: synthetic dataset of the polar region -60 - -90, in the mean calculation everything is proper and nans are ignored. std still looks suspicious.

```python import xarray as xr import glob import numpy as np

data = xr.open_dataset(r"test.nc") data.mean(dim="time", skipna=True).to_netcdf(r"mean_test.nc") python-traceback C:\Users\atraumue\AppData\Local\Continuum\anaconda3\lib\site-packages\dask\array\numpy_compat.py:28: RuntimeWarning: invalid value encountered in true_divide x = np.divide(x1, x2, out) ```

python data.std(dim="time", skipna=True,ddof=1).astype(np.float64).to_netcdf(r"std_test.nc") python-traceback C:\Users\atraumue\AppData\Local\Continuum\anaconda3\lib\site-packages\dask\array\reductions.py:386: RuntimeWarning: invalid value encountered in true_divide u = total / n

Dropbox to files: https://www.dropbox.com/sh/yuf114u143mj2l3/AABuQfC5wu4nrWDH4GsGgFyJa?dl=0

 
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