introduce group scatter attributes

[archmoj]

Resolves #4913.
@plotly/plotly_js

[LiamConnors]

@archmoj, I know we talked about group legend items that would avoid this, but I wonder if the scatter group going back to the centre when you click it on the legend is the right behaviour here and why it would differ to the behaviour for bar.

[archmoj]

@LiamConnors now with the implementation of the alignmentgroup & offsetgroup for scatter trace, you could maintain initial positions. See 918068d as an example.

[alexcjohnson]

@archmoj this looks great! There's one piece I don't understand: if I load zz-scatter-grouping-vs-defaults, then clear all the alignmentgroup attrs - Plotly.restyle(gd,'alignmentgroup',null) - then the traces in the upper right subplot disappear. They also disappear if I set the alignmentgroup for just those two traces to 'bottom' to match the ones below - Plotly.restyle(gd,'alignmentgroup','bottom', [3,9]).

If I also clear offsetgroup they come back, and if I set the offsetgroup for those two to something explicit they get their own group.

So I guess the odd case is when alignmentgroup is either all null or all the same but one trace, in a different subplot from the others, doesn't have an offsetgroup.

There's a related case that's clearly broken: in the same mock, if I just clear offsetgroup for the last trace it stays where it was. But if I first give it a new offsetgroup (so it correctly gets new space) and THEN clear it, it gets pushed into the next group!

Plotly.restyle(gd, 'offsetgroup', null, 11) // clear the group for the last trace, this is OK

Plotly.restyle(gd, 'offsetgroup', '3', 11) // put it in a new group
Plotly.restyle(gd, 'offsetgroup', null, 11) // clear its group

I don't think this is unique to scatter, I can get a similar history-dependent errors from bars from setting / clearing the offsetgroup of the FIRST bar in the bottom right subplot (ie replace the 11 with 4 in those commands). Maybe we just treat null as its own offsetgroup if there are other traces with an offsetgroup on the same axis?

[alexcjohnson]

💃 Actually, since the bug I identified - when there are some traces with offsetgroup and others without it - was already there with bars, I guess it's fine if we merge as is, and just make an issue to come back to this behavior later. Great work!

[Braintelligence]

In case anyone stumbles upon this change and wonders why it doesn't work for them in a horizontal barchart: Make sure your scatter traces also have orientation: "h" or else it won't work. I only found this out while looking through all the comments surrounding this change; I believe it is not mentioned in the documentation at offsetgroup and there is also no example with horizontal orientation within the example made for the Python news article.

[LiamConnors]

Thanks for the feedback @Braintelligence - just to clarify, is the following demonstrating the type of behaviour you are talking about?

I'll add an example to the docs to clarify using with orientation: "h"

import plotly.graph_objects as go
from plotly import data

df = data.tips()[data.tips()["day"] == "Sun"]

mean_values_df = df.groupby(by=["sex", "smoker"], as_index=False).mean(
    numeric_only=True
)

smoker_mean = mean_values_df[mean_values_df.smoker == "Yes"].sort_values(
    by="tip", ascending=False
)
non_smoker_mean = mean_values_df[mean_values_df.smoker == "No"].sort_values(
    by="tip", ascending=False
)

smoker = df[df.smoker == "Yes"].sort_values(by="tip", ascending=False)
non_smoker = df[df.smoker == "No"].sort_values(by="tip", ascending=False)

fig = go.Figure(
    layout=dict(
        xaxis=dict(categoryorder="category descending"),
        scattermode="group",
        legend=dict(groupclick="toggleitem"),
    )
)

fig.add_trace(
    go.Bar(
        orientation='h',
        x=smoker_mean.tip,
        y=smoker_mean.sex,
        name="Average",
        marker_color="IndianRed",
        offsetgroup="smoker",
        legendgroup="smoker",
        legendgrouptitle_text="Smoker",
    )
)


fig.add_trace(
    go.Scatter(
        orientation='h',
        x=smoker.tip,
        y=smoker.sex,
        mode="markers",
        name="Individual tips",
        marker=dict(color="LightSlateGrey", size=5),
        offsetgroup="smoker",
        legendgroup="smoker",
    )
)

fig.add_trace(
    go.Bar(
        orientation='h',
        x=non_smoker_mean.tip,
        y=non_smoker_mean.sex,
        name="Average",
        marker_color="LightSalmon",
        offsetgroup="non-smoker",
        legendgroup="non-smoker",
        legendgrouptitle_text="Non-Smoker",
    )
)


fig.add_trace(
    go.Scatter(
        orientation='h',
        x=non_smoker.tip,
        y=non_smoker.sex,
        mode="markers",
        name="Individual tips",
        marker=dict(color="LightSteelBlue", size=5),
        offsetgroup="non-smoker",
        legendgroup="non-smoker",
    )
)

fig.show()