issues: 462424005

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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
462424005 MDU6SXNzdWU0NjI0MjQwMDU= 3066 xarray rolling does not match pandas when using min_periods and reduce 4903456 open 0     2 2019-06-30T16:44:09Z 2021-02-18T21:41:57Z   NONE      

MCVE Code Sample

MCVE ```python

import numpy as np import pandas as pd import xarray

def custom(x, axis=0): return np.mean(x, axis)

d = pd.DataFrame(np.random.rand(100,3)) r = d.rolling(10, min_periods=5).apply(custom) print(r.iloc[0:10,:])

xd = d.to_xarray().to_array() r = xd.rolling(index=10, min_periods=5).reduce(custom) print(r[:,0:10]) r = xd.rolling(index=10, min_periods=1).reduce(custom) print(r[:,0:10])

```

Problem Description

I am applying a custom function on rolling windows with specific min_periods. The output of pandas..rolling.apply matches what I expect; however, the output of xarray..rolling.reduce doesn't seem to take min_periods into account.

Expected Output and Actual Output

0 1 2 0 NaN NaN NaN 1 NaN NaN NaN 2 NaN NaN NaN 3 NaN NaN NaN 4 0.632168 0.523669 0.543643 5 0.558694 0.565781 0.481204 6 0.559343 0.541787 0.415490 7 0.613457 0.554888 0.398999 8 0.579552 0.496799 0.397681 9 0.562591 0.525096 0.416461 <xarray.DataArray (variable: 3, index: 10)> array([[ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.562591], [ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.525096], [ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.416461]]) Coordinates: * index (index) int64 0 1 2 3 4 5 6 7 8 9 * variable (variable) int64 0 1 2 <xarray.DataArray (variable: 3, index: 10)> array([[ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.562591], [ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.525096], [ nan, nan, nan, nan, nan, nan, nan, nan, nan, 0.416461]]) Coordinates: * index (index) int64 0 1 2 3 4 5 6 7 8 9 * variable (variable) int64 0 1 2

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.8 |Anaconda, Inc.| (default, Dec 29 2018, 19:04:46) [GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] python-bits: 64 OS: Darwin OS-release: 18.6.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.4 libnetcdf: 4.6.1 xarray: 0.12.1 pandas: 0.24.2 numpy: 1.16.4 scipy: 1.2.1 netCDF4: 1.4.2 pydap: None h5netcdf: None h5py: 2.9.0 Nio: None zarr: None cftime: 1.0.3.4 nc_time_axis: None PseudonetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.2.1 dask: 2.0.0 distributed: 2.0.1 matplotlib: 3.1.0 cartopy: None seaborn: 0.9.0 setuptools: 41.0.1 pip: 19.1.1 conda: None pytest: None IPython: 7.5.0 sphinx: None 
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     13221727 issue

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