issue_comments: 239159377

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https://github.com/pydata/xarray/pull/947#issuecomment-239159377 https://api.github.com/repos/pydata/xarray/issues/947 239159377 MDEyOklzc3VlQ29tbWVudDIzOTE1OTM3Nw== 4160723 2016-08-11T13:23:52Z 2016-08-11T15:33:50Z MEMBER

I just made some updates.

I would add an attribute level_names to Coordinate

Done.

It's much cheaper to call .get_level_values() after slicing a MultiIndex than before

Done, although it currently slices an arbitrary number (30) of first elements rather than calculating the number of elements needed for display.

It seems like a fine rule to say that you cannot call .sel on both a level and the dimension name at the same time

Done.

check uniqueness of level names at Dataset/DataArray creation (which is a good idea!)

I tried but it broke some existing tests. It actually triggered data loading for Coordinate objects (via calls to to_index()). I need to further investigate this.

there is not much need for level indexing with a dictionary at all

Right, but in the current implementation this is still used internally.

I would suggest putting the logic to create new variables for levels in the private _get_virtual_variable in dataset.py. [...] If possible, it would be nice if ds['time.day'] works even if time is a multi-index level.

Done. It should also work with multi-index levels although not tested yet.

I'm currently leaning toward Option 3A...

I've chosen option 3A for the repr, but I can change it depending on others' opinions.

What happens when you write ds.coords['level_1'] = ...? [...] probably better to raise an error and note that the MultiIndex should be modified instead.

Done.

Should levels appear in ds.keys() or ds.coords.keys()?

They don't appear in there. If we keep Option 3A for the repr, I also think that we can avoid changes here.

 
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