DataArrayRolling.reduce changes dimensions order

[krvkir]

Seems like a bug.
Code to reproduce:

import numpy as np
import xarray as xr
arr = xr.DataArray(np.random.rand(3, 3, 100))
rolled = arr.rolling(dim_2=3)
print(rolled.mean().dims)
print(rolled.reduce(np.mean).dims)

Output:

('dim_0', 'dim_1', 'dim_2')
('dim_2', 'dim_0', 'dim_1')

P.S. Package version:

$ pip show xarray
---
Metadata-Version: 2.0
Name: xarray
Version: 0.8.2
Summary: N-D labeled arrays and datasets in Python
Home-page: https://github.com/pydata/xarray
Author: xarray Developers
Author-email: xarray@googlegroups.com
Installer: pip
License: Apache
Location: /usr/lib/python3.5/site-packages
Requires: numpy, pandas
Classifiers:
  Development Status :: 4 - Beta
  License :: OSI Approved :: Apache Software License
  Operating System :: OS Independent
  Intended Audience :: Science/Research
  Programming Language :: Python
  Programming Language :: Python :: 2
  Programming Language :: Python :: 2.7
  Programming Language :: Python :: 3
  Programming Language :: Python :: 3.3
  Programming Language :: Python :: 3.4
  Programming Language :: Python :: 3.5
  Topic :: Scientific/Engineering

[shoyer]

I can reproduce this on master.

Indeed, it seems like we need something like GroupBy._restore_dim_order for rolling aggregations.

CC @jhamman

[jhamman]

Agreed. This is not desirable. It should be simple enough to add _restore_dim_order to the Rolling object. @krvkir, care to give it a go?

[krvkir]

@jhamman okay, I'll try to implement this on the next weekend.