issue_comments: 363090775

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https://github.com/pydata/xarray/issues/1092#issuecomment-363090775 https://api.github.com/repos/pydata/xarray/issues/1092 363090775 MDEyOklzc3VlQ29tbWVudDM2MzA5MDc3NQ== 601177 2018-02-05T13:53:55Z 2018-02-05T13:53:55Z NONE

I'm late to the discussion and may be repeating some things essentially already said, but I'd still like to add a further voice.

@shoyer said on 8 Nov 2016:

I am reluctant to add the additional complexity of groups directly into the xarray.Dataset data model. For example, how do groups get updated when you slice, aggregate or concatenate datasets? The rules for coordinates are already pretty complex.

If you prepend the paths to all the names (of dimensions, coordinate variables, and variables) and use the resulting strings as names, don't you just get a collection that would fit right in a xarray.Dataset? (Perhaps I'm just repeating what @lamorton said on 28 Mar 2017.) My feeling is that the only thing missing would be coordinate variables defined in a group closer to the root of the hierarchy, but that needs to be dealt with anyway if you want to read from netCDF4 files correctly (see my #1888). My guess would be that having groups inherit all the dimensions/coordinates of their parent that they do not redefine should be the way to go.

My use case is data from a single metmast over time. There are various instruments measuring all kinds of variables of which 10-minute statistics are recorded. I use groups to keep an overview. (I use something like /[wind|air|prec]/<device>/<variable>, /<device>/<variable>, or /<device>/<variable>/statistic as a hierarchy.) Slicing along the time axis for the whole hierarchy would make perfect sense.

@shoyer said on 30 Mar 2017:

We would possibly want to make another Dataset subclass for the sub-datasets to ensure that their variables are linked to the parent, e.g., xarray.LinkedDataset. This would enable ds['flux']['poloidal'] = subset.

But I'm also not convinced this is actually worth the trouble given how easy it is to write ds['flux', 'poloidal'].

I would prefer the former option, as it more clearly shows the hierarchical nature. If also copying the netCDF4-path-separator-convention, then ds['flux/poloidal'] is shorter than ds['flux', 'poloidal']. (Allowing Dataset or DataArray to have names that include '/' would be dangerous anyway in view of netCDF4 serialization.)

 
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