event when clicking a name in the legend of a plotly's graph in R Shiny

Question

I want to display some information when the user click on the legend of a plotly graph. For example in the code below, if the user clicks on the \"drat\" name in the legend

Answer 1

Just for the sake of completeness: The same can be done without additional JS using plotlyProxy:

library(shiny)
library(plotly)

ui <- fluidPage(
  plotlyOutput("plot"),
  verbatimTextOutput("clickedLegendItem"),
  verbatimTextOutput("doubleclickedLegendItem")
)

server <- function(input, output, session) {
  
  output$plot <- renderPlotly({
    p <- plot_ly(source = "mySource")
    for(name in c("drat", "wt", "qsec"))
    {
      p = add_markers(p, x = as.numeric(mtcars$cyl), y = as.numeric(mtcars[[name]]), name = name)
    }
    p %>% event_register('plotly_legendclick') %>% event_register('plotly_legenddoubleclick')
  })
  
  myPlotlyProxy <- plotlyProxy("plot")
  
  legendClickEvents <- reactive({
    event_data(source = "mySource", "plotly_legendclick")
  })
  
  legendDoubleclickEvents <- reactive({
    event_data(source = "mySource", "plotly_legenddoubleclick")
  })
  
  output$clickedLegendItem <- renderPrint({
    clickedItem <- legendClickEvents()$name
    if (is.null(clickedItem)){"Clicked item appears here"} else {clickedItem}
  })
  
  output$doubleclickedLegendItem <- renderPrint({
    doubleclickedItem <- legendDoubleclickEvents()$name
    if (is.null(doubleclickedItem)){"Doubleclicked item appears here"} else {doubleclickedItem}
  })
}

shinyApp(ui, server)

Answer 2

library(plotly)
library(shiny)
library(htmlwidgets)

js <- c(
  "function(el, x){",
  "  el.on('plotly_legendclick', function(evtData) {",
  "    Shiny.setInputValue('trace', evtData.data[evtData.curveNumber].name);",
  "  });",
  "}")


ui <- fluidPage(
  plotlyOutput("plot"),
  verbatimTextOutput("legendItem")
)

server <- function(input, output, session) {

  output$plot <- renderPlotly({
    p <- plot_ly()
    for(name in c("drat", "wt", "qsec"))
    {
      p = add_markers(p, x = as.numeric(mtcars$cyl), y = as.numeric(mtcars[[name]]), name = name)
    }
    p %>% onRender(js)
  })

  output$legendItem <- renderPrint({
    d <- input$trace
    if (is.null(d)) "Clicked item appear here" else d
  })
}

shinyApp(ui, server)