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/issues/623#issuecomment-147962600,https://api.github.com/repos/pydata/xarray/issues/623,147962600,MDEyOklzc3VlQ29tbWVudDE0Nzk2MjYwMA==,3404817,2015-10-14T07:33:44Z,2015-10-14T07:33:44Z,CONTRIBUTOR,"Alright, I see. In that case we should not create an entirely new syntax for this - unless there are more people than just me interested in this feature. I can just use my own little convenience function that generates a series of array indices that can be fed to `isel`, something like this:

``` python
def wrap_iselkw(ds, dim, istart, istop):
    """"""Returns a kw dict for indices from `istart` to `istop` that wrap around dimension `dim`""""""
    n = len(ds[dim])
    if istart > istop:
        istart -= n
    return { dim : np.mod(np.arange(istart, istop), n) }
```
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,110979851
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?
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,110979851