`DataArray.to_dataframe()` returns MultiIndex frames instead of DatetimeIndex in Pandas 0.21

[esvhd]

Hi all,

I encountered the following after upgrading to Pandas 0.21. Essentially 2 issues:

1. The problem is when I have a Dataset with one of the coords as pd.DatatimeIndex, calling DataArray.to_dataframe() produced a pd.DataFrame with MultiIndex, rather than DatetimeIndex before the upgrade.

2. DataArray.to_dataframe() also behaves differently comparing to DataArray.to_pandas().

The below example reproduces both issues. Shouldn't both method be returning DatetimeIndex-ed data frames? My current hack is to manually convert the MultiIndex back to DatetimeIndex.

I suspect this is something related to the new Pandas but don't see any obvious links. Would someone be able to shed some light on this?

EDIT: I suspect if this is related to this change: MultiIndex Constructor with a Single Level?

Much appreciated.

import xarray as xr
import numpy as np
import pandas as pd

%load_ext watermark
%watermark -dv -iv

# Output
xarray      0.9.6
numpy       1.13.1
pandas      0.21.0
2017-10-30 

CPython 3.6.0
IPython 6.1.0

ind = pd.date_range('2017-01-01', periods = 10)
data = np.random.rand(10, 2)
da = xr.DataArray(data, coords=[ind, ['a', 'b']], dims=['time', 'name'])
da

# Output
<xarray.DataArray (time: 10, name: 2)>
array([[ 0.898389,  0.450587],
       [ 0.514437,  0.444302],
       [ 0.005995,  0.670285],
       [ 0.50663 ,  0.292316],
       [ 0.120645,  0.585734],
       [ 0.651648,  0.248069],
       [ 0.11054 ,  0.537342],
       [ 0.265794,  0.123329],
       [ 0.282711,  0.366271],
       [ 0.420693,  0.717985]])
Coordinates:
  * time     (time) datetime64[ns] 2017-01-01 2017-01-02 2017-01-03 ...
  * name     (name) <U1 'a' 'b'

# Note the MultiIndex returned here
ds['a'].to_dataframe().index

# Output
MultiIndex(levels=[[2017-01-01 00:00:00, 2017-01-02 00:00:00, 2017-01-03 00:00:00, 2017-01-04 00:00:00, 2017-01-05 00:00:00, 2017-01-06 00:00:00, 2017-01-07 00:00:00, 2017-01-08 00:00:00, 2017-01-09 00:00:00, 2017-01-10 00:00:00]],
           labels=[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]],
           names=['time'])

# calling to_panads() returned `DatetimeIndex` as expected.
da.sel(name='a').to_pandas().index

# Output
DatetimeIndex(['2017-01-01', '2017-01-02', '2017-01-03', '2017-01-04',
               '2017-01-05', '2017-01-06', '2017-01-07', '2017-01-08',
               '2017-01-09', '2017-01-10'],
              dtype='datetime64[ns]', name='time', freq='D')

[fmaussion]

There was a recent PR about pandas compatibility (#1669), but I'm not sure if it solves your issue. Could you try your code on latest master?

(pip install --upgrade git+https://github.com/pydata/xarray.git)

[shoyer]

Thanks for the report. This was fixed by #1548 and will be in the next release (release candidate should be out later today).

[esvhd]

Thank you guys!