Some charts rendering differently on master branch vs Plotly.py 5.24.1

[LiamConnors]

There are a few charts that show differently with what's on master branch vs the latest release of Plotly.py:

1. Histogram with px

import plotly.express as px
tips = px.data.tips()
fig = px.histogram(
    tips, x="total_bill", y="tip", color="sex", marginal="rug", hover_data=tips.columns
)
fig.show()

5.24.1:

Master branch:

2. Timeline with px

import pandas as pd
import plotly.express as px
df = pd.DataFrame(
    [
        dict(Task="Job A", Start="2009-01-01", Finish="2009-02-28"),
        dict(Task="Job B", Start="2009-03-05", Finish="2009-04-15"),
        dict(Task="Job C", Start="2009-02-20", Finish="2009-05-30"),
    ]
)
fig = px.timeline(df, x_start="Start", x_end="Finish", y="Task", color="Task")
fig.show()

5.24.1:

Master branch:

3. Scatter with px

iris = px.data.iris()
fig = px.scatter(
    iris,
    x="sepal_width",
    y="sepal_length",
    color="species",
    marginal_y="rug",
    marginal_x="histogram",
)
fig.show()

5.24.1:

Master branch:

[emilykl]

OK, I've confirmed that at least the histogram case is indeed a result of plotly/plotly.js#7009.

Before 7009, when barmode was set to relative, the offsetgroup property of traces was ignored (as far as I am aware). 7009 introduced a change where offsetgroup is applied in relative barmode (and bars with the same category-axis value and offsetgroup are stacked), which has the effect that if two traces have different offsetgroup values, they appear as grouped bars even if barmode is set to relative or stacked.

This caused the change in behavior we are seeing for histograms, since px assigns an offsetgroup to each trace when creating the figure object.

Maybe the fix is as simple as removing offsetgroup from the traces in the generated figure object -- I'm not sure whether there's a reason for it to be there; still investigating.