issue_comments: 147727880

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https://github.com/pydata/xarray/issues/623#issuecomment-147727880 https://api.github.com/repos/pydata/xarray/issues/623 147727880 MDEyOklzc3VlQ29tbWVudDE0NzcyNzg4MA== 3404817 2015-10-13T14:17:08Z 2015-10-13T14:17:08Z CONTRIBUTOR

@jhamman You guys seem to be always ahead of me - which is great! (I just did not notice it this time before I raised the issue...)

But it would actually not be that hard to make selecting regions across the boundary of a circular dimension more convenient in xray.

It would of course be great if it worked with real coordinate (longitude) values:

ds.sel(lon=slice(-90, 15))

which, however, only works if the axis explicitly covers this range (e.g. has range -180E to 180E). If it ranges, say, from 0E to 360E, an empty DataArray is returned. There is no nice way of resolving this, I guess, because you would need to hard-code 360 or have it as a clumsy, non-CF-standard parameter and transform all values to some common range before trying to find the requested region.

But it should be less problematic with

ds.isel(lon=slice(-100, 200))

i.e. isel with negative slice start. As it is now, this also returns an empty DataArray for me (xray 0.6.0), which is in a way consistent with the sel behaviour. But asking for negative indices is actually a quite pythonic way of implying circular. So could this be implemented, now that netCDF4 supports non-contiguous indexing?

 
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