extent parameter in `transform_regression not working as expected

[thomascamminady]

I took this example from the gallary

import altair as alt
import pandas as pd
import numpy as np

np.random.seed(42)
x = np.linspace(0, 10)
y = x - 5 + np.random.randn(len(x))

df = pd.DataFrame({'x': x, 'y': y})

chart = alt.Chart(df).mark_point().encode(
    x='x',
    y='y'
)

chart + chart.transform_regression('x', 'y').mark_line()

and got this plot

So far, so good. But when I add the extent parameter like such

chart + chart.transform_regression('x', 'y',extent=[0,20]).mark_line()

The plot is wrong:

[jonmmease]

Hi @thomascamminady, unfortunately this is an upstream bug in Vega-Lite (reported in vega/vega-lite#9230) that hasn't been investigated yet. Going to close here as we won't be able to address it in Vega-Altair.

I added a comment with some observations in vega/vega-lite#9230 (comment)

[thomascamminady]

Thanks for the info!