Include info from all multi-selection polygons in `plotly_selected` event data

[etpinard]

Hi, I hope all of you are doing well! I'm glad to see @archmoj's leading the v2 push 🚀

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I'm currently rewriting an internal app using Dash.jl and I came across a situation where (I think) common dash callback logic could be greatly simplified with a small plotly.js tweak.

From https://jsbin.com/piveyuniso/edit?html,js,output, we can see that in the plotly_selected event data after a multi-selection interaction, the range.x / range.y coordinates (only!) correspond to the most recent selection.

In situations where we need to consider all the selected regions (i.e. not just the most recent one), we need to accumulate the coordinates from the individual plotly_selected events. This is of course very much doable in dash, but also a little annoying.

Probably the easiest and least-invasive solution would be to add a new plotly_selected event data field named e.g. rangeMulti (and lassoPointsMulti for dragmode: 'lasso') so that:

gd.on('plotly_selected, d => 
  d.rangeMulti.x // [[x00, x01], [x10, x11], ...]
  d.rangeMulti.y // [[y00, y01], [y10, y11], ...]
  // and for 'lasso'
  d.lassoPointsMulti.x // [[Xs of first lasso selection], [Xs of 2nd ...], ...]
  d.lassoPointsMulti.y // [[Ys of first lasso selection], [Ys of 2nd ...], ...]
)

Let me know if this solution makes sense! I can happily open a PR that implements it.

Cheers!

[nicolaskruchten]

Nice to hear from you! This seems like a good solution :)

[archmoj]

@etpinard thanks very much for the note and opening the issue to reach 1K-issue milestone : )

Hope you are doing well and we can't wait to have your PR up!

Whereas with selections I think one could add or remove point to/from selection; I was wondering how your multi suggestion could handle the case of removal? Can't we just call the current behaviour a bug instead?

[nicolaskruchten]

@etpinard are you still planning on opening a PR for this?

[etpinard]

When trying to implement this, I realised things were trickier than expected.

At first, I thought this ticket would "only" require us to write a version of this fillRangeItems statement

plotly.js/src/plots/cartesian/select.js

Line 309 in 3f33829

fillRangeItems(eventData, currentPolygon, filterPoly);

with mergedPolygons instead of currentPolygon. While making this work would be possible and not too difficult, there are a few issues:

• mergedPolygons contains the merged polygons x/y coordinates, not the set of selected rectangles (or ranges). For example, after

mergedPolygons contains the x/y coordinates of 8 vertices, not two [[x0,y0], [x1,x2]] sets corresponding to two selected rectangles.

So, if we choose to use mergePolygons data in the selection event data, we should probably not name the new event data key rangeMulti. Something like polygon.(x|y) would be better.

• If we want to include the set of selected ranges in the event data, we'll need to a new to keep track of them separately in a new dragOptions field.

[archmoj]

There might be cases to end up with multiple polygons too e.g. if one deselect areas from inside a selection.

[nicolaskruchten]

It seems to me that in cases of multiple selections, we should provide as much information as possible to downstream Dash devs:

• range and lassoPoints should contain x2, y2 etc for additional box selections
• range and lassoPoints should contain sign, sign2 etc to indicate inclusion/exclusion
• a new selectionOrder key should contain a list of range, lasso to be able to reconstruct the selection order that the user used
• a mergedPolygons key should contain a list of disjoint merged polygons if folks want to use that instead of reconstructing either shapes or intersection calculations from the above

[archmoj]

Dear @etpinard,
Thanks very much for the note on #6243.
In the event data after v2.13.0, points include all the selected points on all subplots. The range value still includes the last selection. But all the selections inputs are also provided in the plotly_selected event data which can include multi-region path strings.
Do you think this is enough information to work with?

[gvwilson]

Hi - we are trying to tidy up the stale issues and PRs in Plotly's public repositories so that we can focus on things that are still important to our community. Since this one has been sitting for several years, I'm going to close it; if it is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. Thanks for your help - @gvwilson