issues: 1812188730

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1812188730 I_kwDOAMm_X85sA846 8004 Rotation Functional Index example 35968931 open 0     2 2023-07-19T15:23:20Z 2023-08-24T13:26:56Z   MEMBER      

Is your feature request related to a problem?

I'm trying to think of an example that would demonstrate the "functional index" pattern discussed in https://github.com/pydata/xarray/issues/3620.

I think a 2D rotation is the simplest example of an analytically-expressible, non-trivial, domain-agnostic case where you might want to back a set of multiple coordinates with a single functional index. It's also nice because there is additional information that must be passed and stored (the angle of the rotation), but that part is very simple, and domain-agnostic. I'm proposing we make this example work and put it in the custom index docs.

I had a go at making that example (notebook here) @benbovy, but I'm confused about a couple of things:

1) How do I implement .sel in such a way that it supports indexing with slices (i.e. to crop my image) 2) How can I make this lazy? 3) Should the implementation be a "MetaIndex" (i.e. wrapping some pandas indexes)?

Describe the solution you'd like

No response

Describe alternatives you've considered

No response

Additional context

This example is inspired by @jni's use case in napari, where (IIUC) they want to do a lazy functional affine transformation from pixel to physical coordinates, where the simplest example of such a transform might be a linear shear (caused by the imaging focal plane being at an angle to the physical sample).

 
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