add _real_ stacked area charts [feature request]

[salim-b]

I'm filing this issue as a gathering point for the feature request of real stacked area charts.

The current solution to create stacked area charts is to plot cumulative variables which has multiple drawbacks:

• correct (i. e. non-cumulative) hover values have to be set manually by using text = ...
• the resulting chart is incorrect if some traces are shown and others hidden (by clicking on legend items)

A real solution would be to have an argument like layout(linemode = "stack"), same as there is for bar charts. Of course this would need some under-the-hood work in plotly.js first I guess.

Some more information:

• relevant bug reports:
  • plotly.js: Stacked Area Functionality plotly.js#344
  • plotly for R: Example code of stacked fill area  #686
• Generating a stacked area chart in ggplot2 and then converting it to plotly using ggplotly doesn't work as supposed either (the plot doesn't get rescaled correctly if traces in between are unselected, there will just be space left).
• workaround (in JS): https://codepen.io/etpinard/pen/yOgdOb

[cpsievert]

This is more of a feature request of plotly.js, rather than R package. Please file an issue there -- https://github.com/plotly/plotly.js

[salim-b]

ok, reported.