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Dimension order produced by Rechunk is opaque and not controllable; mismatch can cause errors from subsequent ChunksToZarr.

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
python

Research direction

Start by tracing the Rechunk-to-ChunksToZarr pipeline described in the report and reproduce the shown dimension-order mismatch. Compare the dimensions emitted by Rechunk with those expected by the ChunksToZarr template; done means the ordering can be controlled or equivalent dimensions are safely handled before writing.

Written by the indexing model from the issue text.

Description

In a pipeline in which Rechunk is followed by ChunksToZarr, one can run into errors when the dimension order of variables output by Rechunk doesn't match that of the template you pass to ChunksToZarr, resulting in errors like:

ValueError: variable 'geopotential_quantiles' already exists with different dimension names ('hour', 'dayofyear', 'level', 'latitude', 'longitude', 'quantile') != ('level', 'hour', 'dayofyear', 'latitude', 'longitude', 'quantile'), but changing variable dimensions is not supported by to_zarr().

As far as I can tell Rechunk doesn't allow you to control the output dimension order (at least, not on a per-variable basis, which may be necessary to match a given template). An alternative could be to transpose the output template instead to match whatever Rechunk is going to produce, but it's hard to know what that's going to be as well.

As another way around this, it'd be nice if ChunksToZarr could just do the transpose rather than complain if it finds this kind of dimension mismatch (same dimensions in a different order).

Dominant language
Python
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170
Forks
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Avg merge
18h 27m
Merged PRs (30d)
1

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