Improvements to algorithm for attaching key attribute for shiny's event data, fixes #1610

[cpsievert]

Fixes #1610. Note also that when pt.pointNumbers is populated, the key attribute is relayed properly

Testing notes

Install remotes::install_github("ropensci/plotly"), then run the app below. As you hover over points, information about the hovered point should appear in the R console.

library(shiny)
library(plotly)

ui <- fluidPage(
  plotlyOutput("distPlotTest")
)

server <- function(input, output) {
  
  output$distPlotTest <- renderPlotly({
    highlight_key(mtcars, ~carb) %>%
      plot_ly(x = ~mtcars$carb, key = ~row.names(mtcars), type = "histogram") %>%
        layout(barmode = "overlay") %>% 
        highlight(on = "plotly_hover", off="plotly_deselect") 
  })
  
  observe({
    print(event_data("plotly_hover"))
  })
  
}

# Run the application
shinyApp(ui = ui, server = server)

[schloerke]

Missing logic from this line: https://github.com/ropensci/plotly/pull/1611/files#diff-0ad25a6dcc3b90b388d12e866865156fL269