Assigning customdata for Scattermapbox lines

[radumas]

I'm trying to use the click/hover callbacks in dash with a mapbox map that displays lines. I create each line with something like

go.Scattermapbox(
        lat=lats,
        lon=lons,
        mode='lines',
        hoverinfo='text',
        name=row.segment_name,
        customdata=row.segment_id,
        text=row.segment_id,
        showlegend=False

segment_id or segment_text appear nicely on hover, however in printing the callback I notice that the contents are

{
  "points": [
    {
      "lat": 43.6464730064524,
      "curveNumber": 2,
      "lon": -79.4037543398975,
      "pointNumber": 28
    }
  ]
}

Is there a way to link curveNumber back to the data that created the map? If I assign a numeric variable to customdata, it doesn't appear in the callback. If I assign a string variable to customdata, only 1 letter appears per point on the line.

Current workaround

My understanding is that whatever is consuming the customdata is iterating over it for each generating point. I tried creating an iterator for the variable I want that iterates infinitely, but this gave me errors that repeat() is not JSON seriablizable. So my workaround is to create a list from repeating the segment_id variable for the number of points there are in the line.

customdata=list(itertools.repeat(row.segment_id, times=len(lats))),

[cldougl]

Hi there,
For dash support you can checkout our forum here: https://community.plot.ly/c/dash

[radumas]

While my problem with this occurred in Dash, customdata is actually part of the plotly.py API
👉 https://plot.ly/python/reference/#scattermapbox-customdata

[cldougl]

Right, but for callback issues and questions you'd have to refer to the dash repo or plotly.js repo

If you encounter a bug with the attribute customdata in relation to the graph created with the python api I'm happy to address it here, otherwise we ask users to ask support questions in the forum or via our support app

[radumas]

Realizing that I didn't explain my problem with customdata and lines properly ☝️

For lines in scattermapbox, customdata is being treated as an array, and is assigning one item of that array to each point of the line, rather than the line as a whole. Also, if customdata is assigned a number, this assignment appears to fail silently, which doesn't seem ideal. This wasn't intuitive to me, and isn't explicit in the documentation.

Assigns extra data each datum. This may be useful when listening to hover, click and selection events. Note that, "scatter" traces also appends customdata items in the markers DOM elements

The documentation should make this behaviour explicit for lines. Also I'd recommend that, if mode='lines', string or numeric values assigned to customdata should be automatically repeated for every point on a line.

[cldougl]

I see, assigning one customdata item to each point of the line is the expected behaviour. Based on the description we try to make it clear that this takes a list rather than single value,

but if you have suggestions on how to make that more clear it's definitely welcome-thanks!

Also, if you're interested in setting a consistent item across all points in a line you may want to consider the text attribute: https://plot.ly/python/reference/#scattermapbox-text (it looks like you may have added that in your code above, that can be set to a string and then attributed to all points in a line)

[radumas]

Unfortunately the text attribute doesn't get passed in a callback (but that's a Dash issue I guess).

Can I suggest something like the following change to the doc?

Assigns each item from the customdata array as extra data to each mapped datum. This may be useful when listening to hover, click and selection events. For lines, these data are assigned to the line's component points. Note that, "scatter" traces also append customdata items in the markers DOM elements