Multiple legends: trace.legend and layout.legend<N>

Breaking off of https://github.com/plotly/plotly.js/issues/1668 …

Multiple users have requested what amounts to the ability to have multiple legends, within the current concept of “each trace has a single legend item which appears in a single legend”. This could be implemented by adding a legend attribute to each trace that would operate similarly to the xaxis attribute, and a corresponding legend2, legend3 series of attributes in the layout. This is distinct from the idea of having a legend for size and one for symbol etc, as in that case each item would refer to multiple traces, and each trace would be represented by multiple items.

The major challenge here is the default positioning of legend2 if present… we could do something really ugly like just having it default to the position of the first legend and forcing users to position them manually, but having it “stick to the bottom” is probably a much more graceful solution, if more complex to implement.

[nicolaskruchten]

We’re still looking for a sponsor, and will update this issue when we find one 😃

[nicolaskruchten]

This issue has been tagged with NEEDS SPON$OR

A community PR for this feature would certainly be welcome, but our experience is deeper features like this are difficult to complete without the Plotly maintainers leading the effort.

Sponsorship range: $10k-$15k

What Sponsorship includes:

• Completion of this feature to the Sponsor’s satisfaction, in a manner coherent with the rest of the Plotly.js library and API
• Tests for this feature
• Long-term support (continued support of this feature in the latest version of Plotly.js)
• Documentation at plotly.com/javascript
• Possibility of integrating this feature with Plotly Graphing Libraries (Python, R, F#, Julia, MATLAB, etc)
• Possibility of integrating this feature with Dash
• Feature announcement on community.plotly.com with shout out to Sponsor (or can remain anonymous)
• Gratification of advancing the world’s most downloaded, interactive scientific graphing libraries (>50M downloads across supported languages)

Please include the link to this issue when contacting us to discuss.