Type checking in plotlyProxy()

[woodwards]

I came across this "bug" in a comment on stackoverflow while I was trying to get addTrace working.

https://stackoverflow.com/questions/50620360/using-proxy-interface-in-plotly-shiny-to-dynamically-change-data

I can comfirm that this seems to be the case. addTrace should work even with 0 points in the trace I think, since you might want to add point later.

[cpsievert]

That SO question is really about Plotly.restyle(), but I get your point...

It's important to know that when you use plotlyProxy(), you're working directly with plotly.js, and plotly.js is more strict about values than plot_ly() and ggplotly().

For example if you look at the data (i.e., traces) component behind:

plot_ly(x = 1, y = 1) %>% plotly_json()

You'll notice the R package automatically ensures x and y are arrays of length 1. If, instead, these were sent as numerical constants, the plotly.js would throw an error, because it expects them to be arrays. For the same reasoning, Plotly.addTraces() will error if x or y aren't arrays.

That being said, plotlyProxy() could probably be doing more to make the experience more like plot_ly()