"Extent" property for Regression does not modify the regression extent and nullifies the regression.

[chknfr1ed]

I initially posted this in Vega and was suggested to move to here.

When I try to add the "extent" property as listed in the vega-lite documentation, the regression no longer exists and instead the data becomes a line chart.

This is the example pulled from the regression example in the vega-lite documentation:

However, when I add in the extent property to the example, this is the result:

[chknfr1ed]

Someone else is also having this issue from SO: https://stackoverflow.com/questions/77845962/regression-line-issue-in-vegalite-charts

[jonmmease]

When adding this to Vega-Lite:

"transform": [
    {"regression": "IMDB Rating", "on": "Rotten Tomatoes Rating", "extent": [0, 100]}
],

The generated Vega ends up with this transform:

    {
      "name": "data_1",
      "source": "source_0",
      "transform": [{"type": "extent", "field": [0, 100]}]
    },

This is nonsensical, as [0, 100] is not a field, and the extent transform doesn't bind the result to a signal anyway, so even if the "field" were valid, it wouldn't do anything.

@vega/maintainers Does anyone have context on how this is supposed to work in terms of the generated Vega? It seems to me like this needs to be a configuration option in the Vega transform, and it's not clear to me how this ever worked.

[thomascamminady]

FWIW, I filed the issue on altair's end here: vega/altair#3347

I was certain that this used to work and it seems that with altair=5.0.0 this is working as expected, but with altair=5.1.0 this does not work properly.

Looking at the release notes for 5.1.0 (https://github.com/altair-viz/altair/releases/tag/v5.1.0) this corresponds to the vega-lite update from version 5.8.0 to version 5.14.1.

Comparing both vega-lite versions can done here: v5.8.0...v5.14.1

I think I'm unable to pinpoint this further, but maybe this insight helps someone else :)

[player1537]

I can confirm that when I test with:

<script src="https://cdn.jsdelivr.net/npm/vega@5.25.0/build/vega.js"></script>
<script src="https://cdn.jsdelivr.net/npm/vega-lite@5.9.3/build/vega-lite.js"></script>
<script src="https://cdn.jsdelivr.net/npm/vega-embed@6.22.2/build/vega-embed.js"></script>

and vary the vega-lite version, then v5.9.3 works, and v5.10.0 does not work. (They all "work", but the latter has the bug this thread is about)

This brings the relevant changeset down to: v5.9.3...v5.10.0

Edit: After digging a little, the only relevant change is "feat: add extent transform (#8940)"

Some of the tests look an awful lot like the bug happening here.

{
    ...
      "transform": [{"extent": "b", "param": "b_extent" }],
    ...
}

->

{
    ...
      "transform": [{"type": "extent", "field": "b", "signal": "b_extent"}]
    ...
}

I think this might be a simple naming collision. The code for dealing with the extent transform is getting applied to the regression's extent property.

[lsh]

I see the issue. Will put up a fix ASAP.