html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/pull/337#issuecomment-76483784,https://api.github.com/repos/pydata/xarray/issues/337,76483784,MDEyOklzc3VlQ29tbWVudDc2NDgzNzg0,1217238,2015-02-27T22:22:47Z,2015-02-27T22:22:47Z,MEMBER,"> Should season be listed in the ""virtual variables"" here: http://xray.readthedocs.org/en/latest/data-structures.html

Good catch

> With the addition of the nan-safe functions, numpy is throwing a lot of warnings for things like ""empty slices"" (ocean grid cells in my example never have data). Its not a big deal to silence them but it is a bit annoying.

To fix this, you can install bottleneck (which will also make these operations much faster). We could also look into silencing the warnings. I'll add a note to the documentation somewhere.

> Since ds.groupby('time.season').mean('time') returns a Dataset with a Coordinates variable named time.season, ds.sel(time.season='JJA') doesn't work for Python syntax reasons. So, I don't know if I would change the syntax used in my example (selecting my position). I'm not keen on this constructor: ds.sel(**{'time.season':'JJA'}). I'm wondering if it would be better to name the coordinates returned from ""virtual variable"" operations without the ""time."" portion. Just a thought.

This one is trickier. Let me make a new issue.
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https://github.com/pydata/xarray/pull/337#issuecomment-76448604,https://api.github.com/repos/pydata/xarray/issues/337,76448604,MDEyOklzc3VlQ29tbWVudDc2NDQ4NjA0,2443309,2015-02-27T18:44:55Z,2015-02-27T18:44:55Z,MEMBER,"@shoyer: I just ran the example and it still works without any modifications.

A few comments/questions:
- Should `season` be listed in the ""virtual variables"" here:  http://xray.readthedocs.org/en/latest/data-structures.html
- With the addition of the nan-safe functions, numpy is throwing a lot of warnings for things like ""empty slices"" (ocean grid cells in my example never have data).  Its not a big deal to silence them but it is a bit annoying.
- Since `ds.groupby('time.season').mean('time')` returns a `Dataset` with a `Coordinates` variable named `time.season`, `ds.sel(time.season='JJA')` doesn't work for Python syntax reasons.  So, I don't know if I would change the syntax used in my example (selecting my position).  I'm not keen on this constructor: `ds.sel(**{'time.season':'JJA'})`.  I'm wondering if it would be better to name the coordinates returned from ""virtual variable"" operations without the ""time."" portion.  Just a thought.

I will still get you an updated version of the example.
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https://github.com/pydata/xarray/pull/337#issuecomment-76135102,https://api.github.com/repos/pydata/xarray/issues/337,76135102,MDEyOklzc3VlQ29tbWVudDc2MTM1MTAy,1217238,2015-02-26T07:43:29Z,2015-02-26T07:43:29Z,MEMBER,"CC @jhamman 

It would be awesome if you could update your example to work on xray 0.4 before I do the final release (there will be a release candidate).

I think the main change effecting this example that is that `'time.season'` now returns strings like `'DFJ'`, not integers. See http://xray.readthedocs.org/en/latest/whats-new.html for more details.
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