Unfortunately, this is not a backwards-compatible change... For example, the following:

import plotly.express as px
fig = px.scatter(x=[1,2,3], y=[1,2,3], color=["a","a","a"])
fig.show()

On master this yields

newplot (1)

but on this branch the legend has disappeared and the tooltips no longer include "color=a" etc.

(note: we have "Percy" image tests that compare the graphical output of PRs to that of master, but for some reason these don't run on pull requests from folks outside the Plotly organization. The example I gave above would likely cause this test to fail... the first commit on my PR failed this test as well for similar reasons)

Note: #3761 does appear backwards-compatible because it independently computes sorted_group_names

Oh, I see! I believe it is because of the hard-coding of the orders being {} and the sorted_group_names being [("",....)].
I'll update the logic of constructing orders and sorted_group_names to match the current master behavior

Note: #3761 does appear backwards-compatible because it independently computes sorted_group_names

I guess we both identified the issue at the same time! 😄

OK, this looks great, thanks! I have an idea about how to reuse the existing uniques() call to compute all_same_group more efficiently, but I'll do that on my branch.

Thanks for pushing through this with me :)

Great! And thank you as well @nicolaskruchten for maintaining this amazing library & the quick responses! :)