observablehq / observablehq/plot

Generating extra channels with the group transform?

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enhancement question
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Description

Should it be possible to use the channels option with the group transform (and bin transform)? That way you could generate and group an extra channel that is unknown to the mark. I think currently the channels option simply gets propagated, so you can’t reference an extra channel as a group output.

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading the group and bin transforms and how they handle the channels option. Determine the expected behavior for an extra channel unknown to the mark, then add coverage showing that it can be generated, grouped, and exposed as a group output.

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Assessment

Tech stack
d3
Domain
data-visualization
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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