[BUG]: barmode="group" not working with second y axis

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#5,582 2 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
python
Domain
data-visualization

Research direction

Start by running the inline Python reproducer and opening the generated /tmp/trials.html to compare barmode="group" with traces on separate y axes. Trace the chart-rendering entry point responsible for bar positioning; done means the two traces render side by side rather than stacked, while preserving their secondary-axis settings and error bars.

Written by the indexing model from the issue text.

Description

bug P3 size: 3 
import plotly.graph_objects as go

def bar_chart_with_error_bars():
    # Trace C
    trace_c = go.Bar(
        x=["Trial 1", "Trial 2", "Trial 3"],
        y=[3, 6, 4],
        name="Trace C",
        error_y=dict(
            type="data",
            array=[1, 0.5, 1.5]
        )
    )

    # Trace E (secondary y-axis)
    trace_e = go.Bar(
        x=["Trial 1", "Trial 2", "Trial 3"],
        y=[400, 700, 300],
        name="Trace E",
        yaxis="y2",
        error_y=dict(
            type="data",
            array=[50, 100, 200]
        )
    )

    # Layout
    layout = go.Layout(
        barmode="group",
        yaxis=dict(title="Trace C"),
        yaxis2=dict(
            title="Trace E",
            overlaying="y",
            side="right"
        )
    )

    # Create figure
    fig = go.Figure(data=[trace_c, trace_e], layout=layout)

    # Save to HTML
    fig.write_html("/tmp/trials.html")


# Call the function
bar_chart_with_error_bars()

Resulting chart. Stack instead of group.
Image

rust version is also broken, but in different way - overlay instead of group: https://github.com/plotly/plotly.rs/issues/391

Dominant language
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