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Some notes on alignment with pangeo-forge-recipes around "keys"

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#32 1 comment 4 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Refactor
Clarity
Needs clarification
Activity status
Stale
Tech stack
python

Research direction

Start by reading the Xarray Beam keys documentation and the referenced pangeo_forge_recipes/patterns.py lines 70-114. Compare those abstractions with the project's handling of indexes in FilePatterns and parallel Zarr writing. The issue does not define a concrete change or acceptance criteria, so a maintainer decision is needed before implementation.

Written by the indexing model from the issue text.

Description

At today's Pangeo Forge meeting, @alxmrs told us a bit more about Xarray Beam. I'm happy to note that we are aligning a bit around certain abstractions. I'm not proposing to merge or share code or anything at this stage. Just happy to see that we have independently arrived at some similar concepts. Comparing side by side may also suggest improvements.

Xarray Beam

https://xarray-beam.readthedocs.io/en/latest/data-model.html#keys-in-xarray-beam

To keep track of how individual records could be combined into a larger (virtual) dataset, Xarray-Beam defines a Key object. > Key objects consist of:

  • offsets: integer offests for chunks from the origin in an immutabledict
  • vars: The subset of variables included in each chunk, either as a frozenset, or as None to indicate “all variables”.
Pangeo Forge

We currently call this an "index," although I agree that key is a better name. Our use of indexes is less well documented as it is not really public API but more of an internal thing. We mention it here: https://pangeo-forge.readthedocs.io/en/latest/recipe_user_guide/file_patterns.html#inspect-a-filepattern

The index is its own special type of object used internally by recipes, a pangeo_forge_recipes.patterns.Index, (which is basically a tuple of one or more pangeo_forge_recipes.patterns.DimIndex objects).

The code is pretty straightforward and the comments explain things better.

https://github.com/pangeo-forge/pangeo-forge-recipes/blob/49997cb52cff466bd394c1348ef23981e782a4d9/pangeo_forge_recipes/patterns.py#L70-L114

These indexes are used both by FilePatterns (see #31) as well as for parallel writing of Zarr datasets.

cc @cisaacstern

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