R plotly: how to observe whether a trace is hidden or shown through legend clicks with multiple plots

Question

I am trying to figure out which traces the user hides from a scatter plot by means of deselecting them in the interactive legend of plotly.

I have read this SO post

Answer 1

Does it help?

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);",
  "  });",
  "  el.on('plotly_restyle', function(evtData) {",
  "    Shiny.setInputValue('visibility', evtData[0].visible);",
  "  });",
  "}")

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$legendItem <- renderPrint({
    trace <- input$trace
    ifelse(is.null(trace), 
           "Clicked item will appear here",
           paste0("Clicked: ", trace, 
                  " --- Visibility: ", input$visibility)
    )
  })
}

shinyApp(ui, server)

---

EDIT

There's an issue with the previous solution when one double-clicks on a legend item. Here is a better solution:

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

js <- c(
  "function(el, x){",
  "  var d3 = Plotly.d3;",
  "  el.on('plotly_restyle', function(evtData) {",
  "    var out = {};",
  "    d3.select('g.legend').selectAll('.traces').each(function(){",
  "      var trace = d3.select(this)[0][0].__data__[0].trace;",
  "      out[trace.name] = trace.visible;",
  "    });",
  "    Shiny.setInputValue('traces', out);",
  "  });",
  "}")


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$legendItem <- renderPrint({
    input$traces
  })
}

shinyApp(ui, server)

---

If you have multiple plots, add the plot id in the legend selector, and use a function to generate the JavaScript code:

js <- function(i) { 
  c(
  "function(el, x){",
  "  var id = el.getAttribute('id');",
  "  var d3 = Plotly.d3;",
  "  el.on('plotly_restyle', function(evtData) {",
  "    var out = {};",
  "    d3.select('#' + id + ' g.legend').selectAll('.traces').each(function(){",
  "      var trace = d3.select(this)[0][0].__data__[0].trace;",
  "      out[trace.name] = trace.visible;",
  "    });",
  sprintf("    Shiny.setInputValue('traces%d', out);", i),
  "  });",
  "}")
}

Then do p1 %>% onRender(js(1)), p2 %>% onRender(js(2)), ..., and you get the info about the traces visibility in input$traces1, input$traces2, ....

Another way is to pass the desired name in the third argument of the JavaScript function, with the help of the data argument of onRender:

js <- c(
  "function(el, x, inputName){",
  "  var id = el.getAttribute('id');",
  "  var d3 = Plotly.d3;",
  "  el.on('plotly_restyle', function(evtData) {",
  "    var out = {};",
  "    d3.select('#' + id + ' g.legend').selectAll('.traces').each(function(){",
  "      var trace = d3.select(this)[0][0].__data__[0].trace;",
  "      out[trace.name] = trace.visible;",
  "    });",
  "    Shiny.setInputValue(inputName, out);",
  "  });",
  "}")


p1 %>% onRender(js, data = "tracesPlot1")
p2 %>% onRender(js, data = "tracesPlot2")