issues: 321917084

Code Sample, a copy-pastable example if possible

python import xarray as xr remote_data = xr.open_dataarray('http://iridl.ldeo.columbia.edu/SOURCES/.Models'\ '/.SubX/.RSMAS/.CCSM4/.hindcast/.zg/dods', chunks={'L': 1, 'S': 1}) da = remote_data.isel(P=0,L=0,M=0,X=0,Y=0) da_day_clim = da.groupby('S.dayofyear').mean('S') da_day_clim2 = da_day_clim.chunk({'dayofyear': 366}) da_day_clim_smooth = da_day_clim2.rolling(dayofyear=31, center=True).mean()

Problem description

Initially discussed on SO: https://stackoverflow.com/questions/50265586/xarray-rolling-mean-of-dask-array-conflicting-sizes-for-data-and-coordinate-in

The rolling operation gives a ValueError: conflicting sizes for dimension 'dayofyear': length 351 on the data but length 366 on coordinate 'dayofyear' The length of 351 in the data is created in the rolling operation.

Here's the full traceback: ``` ValueError Traceback (most recent call last) <ipython-input-57-6acf382cdd3d> in <module>() 4 da_day_clim = da.groupby('S.dayofyear').mean('S') 5 da_day_clim2 = da_day_clim.chunk({'dayofyear': 366}) ----> 6 da_day_clim_smooth = da_day_clim2.rolling(dayofyear=31, center=True).mean()

~/anaconda/envs/SubXNAO/lib/python3.6/site-packages/xarray/core/rolling.py in wrapped_func(self, **kwargs) 307 if self.center: 308 values = values[valid] --> 309 result = DataArray(values, self.obj.coords) 310 311 return result

~/anaconda/envs/SubXNAO/lib/python3.6/site-packages/xarray/core/dataarray.py in init(self, data, coords, dims, name, attrs, encoding, fastpath) 224 225 data = as_compatible_data(data) --> 226 coords, dims = _infer_coords_and_dims(data.shape, coords, dims) 227 variable = Variable(dims, data, attrs, encoding, fastpath=True) 228

~/anaconda/envs/SubXNAO/lib/python3.6/site-packages/xarray/core/dataarray.py in _infer_coords_and_dims(shape, coords, dims) 79 raise ValueError('conflicting sizes for dimension %r: ' 80 'length %s on the data but length %s on ' ---> 81 'coordinate %r' % (d, sizes[d], s, k)) 82 83 if k in sizes and v.shape != (sizes[k],):

ValueError: conflicting sizes for dimension 'dayofyear': length 351 on the data but length 366 on coordinate 'dayofyear' ```

Expected Output

The rolling operation would work on the dask array as it would on the dataarray e.g. ``` import pandas as pd import xarray as xr import numpy as np

dates = pd.date_range('1/1/1980', '31/12/2000', freq='D') data = np.linspace(1, len(dates), num=len(dates), dtype=np.float) da = xr.DataArray(data, coords=[dates], dims='time') da_day_clim = da.groupby('time.dayofyear').mean('time') da_day_clim_smooth = da_day_clim.rolling(dayofyear=31, center=True).mean() ```

Output of xr.show_versions()