Fixed index2da causing inverted output

[MgeeeeK]

The issue was occurring because of recent changes in xarray.

Relevant threads:

• to_dataframe/to_series fails when one out of more than one dims are stacked / multiindex pydata/xarray#3008
• Fix DataArray.to_dataframe when the array has MultiIndex pydata/xarray#4442

Closes #399

[MgeeeeK]

@sjsrey @darribas I think its fixed now

[sjsrey]

@sjsrey @darribas I think its fixed now

should we pin to a version of xarray before the breakage, and then change when they release the new version that fixes this?

[MgeeeeK]

@sjsrey @darribas I think its fixed now

should we pin to a version of xarray before the breakage, and then change when they release the new version that fixes this?

Here I was referring to the error that index2da was raising in #399.
Earlier, due to a bug related to MultiIndex in the xarray, I had to sort the data to align it with the indices (the bug was fixed in the latest release v0.17.0 (24 Feb 2021) and therefore, there is no need for sorting)

I can also add support for the previous versions cos this will fail if the users are using xarray<0.17.0 package.