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TomNicholas
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topic-DataTree
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| We cannot store these non-alignable variables on a single :py:class:`~xarray.Dataset` object, because they do not exactly align: |
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I guess it would be more correct to say that we cannot store them unchanged.
max-sixty
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As someone who doesn't use DataTree yet, this is v nice & clear!
…las/xarray into datatree_alignment_docs
Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>
…las/xarray into datatree_alignment_docs
Co-authored-by: Stephan Hoyer <shoyer@google.com>
| Data Alignment | ||
| ~~~~~~~~~~~~~~ |
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TODO: add comment about open_groups being useful if your data doesn't align
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this is the only note I have on open_groups, it probably deserves more. https://github.com/pydata/xarray/blob/main/doc/getting-started-guide/quick-overview.rst?plain=1#L284
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gonna prioritize merging this and improving documentation for open_groups later
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What's here looks good. I think my main question is about the things that are left as TODOs. Do they need to be done in this PR, or could/should they be tracked under a new issue, so this PR can be merged?
doc/user-guide/hierarchical-data.rst
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| .. note:: | ||
| If you were a previous user of the prototype `xarray-contrib/datatree <https://github.com/xarray-contrib/datatree>`_ package, this is different from what you're used to! | ||
| In that package the data model was that nodes actually were completely unrelated. The data model is now slightly stricter. |
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Possible nit (feel free to ignore): Would it be clearer to say the information (or specifically Dataset object) contained on each node was unrelated?
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Yeah that's a great point, it would definitely be both more clear and more accurate to say that instead.
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| This requirement of aligned dimensions is similar to netCDF's concept of `inherited dimensions <https://www.unidata.ucar.edu/software/netcdf/workshops/2007/groups-types/Introduction.html>`_, as in netCDF-4 files dimensions are `visible to all child groups <https://docs.unidata.ucar.edu/netcdf-c/current/groups.html>`_. | ||
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| This alignment check is performed up through the tree, all the way to the root, and so is therefore equivalent to requiring that this :py:func:`~xarray.align` command succeeds: |
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Before getting to this statement, I had added a comment saying we should make it clear that the alignment check ensures alignment with all ancestors, not just the immediate parent. But this covers it nicely!
doc/user-guide/hierarchical-data.rst
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| Coordinate Inheritance | ||
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| Notice that in the trees we constructed above (LINK OR DISPLAY AGAIN?) there is some redundancy - the ``lat`` and ``lon`` variables appear in each sibling group, but are identical across the groups. |
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LINK OR DISPLAY AGAIN
I'm tempted to say display it again after this paragraph.
doc/user-guide/hierarchical-data.rst
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| We can override inherited coordinates with newly-defined ones, as long as those newly-defined coordinates also align with the parent nodes. | ||
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| EXAMPLE OF THIS? WOULD IT MAKE MORE SENSE TO USE DIFFERENT DATA TO DEMONSTRATE THIS? | ||
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| EXAMPLE OF INHERITING FROM A GRANDPARENT? | ||
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| EXPLAIN DEDUPLICATION? |
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Is the plan to include these points in this PR, or merge what is here (maybe with this commented out) and then add more content later?
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I was going to do it in this PR, but given that everyone seems to be happy with what's here already, and this is a natural break point, perhaps I will just merge this for now.
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A follow-up issue could be to "document the subtleties of coordinate inheritance"
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(I had hoped to add these bits before you reviewed it @owenlittlejohns )
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Removed that content for use in a future PR in 6cab6f8
…las/xarray into datatree_alignment_docs
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Adds a dedicated section on datatree alignment and coordinate inheritance to the Hierarchical Data page. Intended to complement what's already been added to the Data Structures page by @flamingbear, in a more narrative form. I've also tried to separate out the concept of alignment from coordinate inheritance.
This shouldn't really be merged until a few other things are fixed, particularly #9499.
Tests addedUser visible changes (including notable bug fixes) are documented inwhats-new.rstNew functions/methods are listed inapi.rstcc @shoyer @eni-awowale @owenlittlejohns