Removing traces by name using plotlyProxy (or accessing output schema in reactive context)

3. Edit: Here is another approach using Shiny.addCustomMessageHandler and Plotly.deleteTraces directly in the onRender call instead of utilizing plotlyProxyInvoke:

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

js <- "function(el, x, data){
         var id = el.getAttribute('id');
         Shiny.addCustomMessageHandler('remove-trace', function(tracename) {
         function getTraceIndices(trace, traceindex) {
           if (trace.name === tracename) {
             Plotly.deleteTraces(id, traceindex);
           }
         }
         x.data.forEach(getTraceIndices);
         });
       }"

ui <- fluidPage(
  textInput("TraceName", "Trace Name"),
  actionButton("Add", "Add Trace"),
  actionButton("Remove", "Remove Trace"),
  plotlyOutput("MyPlot")
)

server <- function(input, output, session) {
  output$MyPlot <- renderPlotly({
    plot_ly(type = "scatter", mode = "markers") %>%
      layout(showlegend  = TRUE) %>% onRender(js) 
  })
  
  observeEvent(input$Add, {
    req(input$TraceName)
    plotlyProxy("MyPlot", session) %>%
      plotlyProxyInvoke("addTraces", list(x = rnorm(10), y = rnorm(10),
                                          type = "scatter", mode = "markers",
                                          name = input$TraceName))
  })
  
  observeEvent(input$Remove, {
    req(input$TraceName)
    session$sendCustomMessage("remove-trace", input$TraceName)
  })
}

shinyApp(ui, server)

2. Edit: by now the Plotly.d3 object was removed from plotly. I updated the JS code accordingly (the trace indices are extracted from plotly's data object).

1. Edit: using plotlyProxy:

Update @SeGa, thanks for adding support to delete traces with duplicated names!

Finally, I found a solution to realize the expected behaviour by adapting this answer. I'm receiving the trace.name / trace.index mapping by using onRender from library(htmlwidgets) after the remove-button is clicked:

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

js <- "function(el, x, inputName){
  el.on('plotly_redraw', function(eventdata) {
    var out = [];
    function getTraceIndices(trace, traceindex) {
      if (typeof trace.name !== 'undefined') {
        var tracename = trace.name ;
      } else {
        var tracename = '';
      }
      out.push([name=tracename, index=traceindex]);
    }
    x.data.forEach(getTraceIndices);
    Shiny.setInputValue(inputName, out);
  });
}"

ui <- fluidPage(
  textInput("TraceName", "Trace Name"),
  verbatimTextOutput("PrintTraceMapping"),
  actionButton("Add", "Add Trace"),
  actionButton("Remove", "Remove Trace"),
  plotlyOutput("MyPlot")
)

server <- function(input, output, session) {
  output$MyPlot <- renderPlotly({
    plot_ly(type = "scatter", mode = "markers") %>%
      layout(showlegend  = TRUE) %>% onRender(js, data = "TraceMapping") 
  })
  
  output$PrintTraceMapping <- renderPrint({unlist(input$TraceMapping)})
  
  observeEvent(input$Add, {
    req(input$TraceName)
    plotlyProxy("MyPlot", session) %>%
      plotlyProxyInvoke("addTraces", list(x = rnorm(10), y = rnorm(10),
                                          type = "scatter", mode = "markers",
                                          name = input$TraceName))
  })
  
  observeEvent(input$Remove, {
    req(input$TraceName, input$TraceMapping)
    traces <- matrix(input$TraceMapping, ncol = 2, byrow = TRUE)
    indices <- as.integer(traces[traces[, 1] == input$TraceName, 2])
    plotlyProxy("MyPlot", session) %>%
      plotlyProxyInvoke("deleteTraces", indices)
  })
}

shinyApp(ui, server)

Result:

Useful articles in this context:

shiny js-events

plotly addTraces

plotly deleteTraces

Solution for Shiny Modules using plotlyProxy:

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

js <- "function(el, x, data){
  $(document).on('shiny:inputchanged', function(event) {
    if (event.name.indexOf('Remove') > -1) {
      var out = [];
      function getTraceIndices(trace, traceindex) {
        if (typeof trace.name !== 'undefined') {
          var tracename = trace.name ;
        } else {
          var tracename = '';
        }
        out.push([name=tracename, index=traceindex]);
      }
      x.data.forEach(getTraceIndices);
      Shiny.setInputValue(data.ns + data.x, out);
    }
  });
}"

plotly_ui_mod <- function(id) {
  ns <- NS(id)
  tagList(
    textInput(ns("TraceName"), "Trace Name"),
    verbatimTextOutput(ns("PrintTraceMapping")),
    actionButton(ns("Add"), "Add Trace"),
    actionButton(ns("Remove"), "Remove Trace"),
    plotlyOutput(ns("MyPlot"))
  )
}

plotly_server_mod <- function(input, output, session) {
  sessionval <- session$ns("")
  
  output$MyPlot <- renderPlotly({
    plot_ly(type = "scatter", mode = "markers") %>%
      layout(showlegend  = TRUE) %>% onRender(js, data = list(x = "TraceMapping", 
                                                              ns = sessionval))
  })
  output$PrintTraceMapping <- renderPrint({unlist(input$TraceMapping)})
  observeEvent(input$Add, {
    req(input$TraceName)
    plotlyProxy("MyPlot", session) %>%
      plotlyProxyInvoke("addTraces", list(x = rnorm(10),y = rnorm(10),
                                          type = "scatter",mode = "markers",
                                          name = input$TraceName))
  })
  observeEvent(input$Remove, {
    req(input$TraceName, input$TraceMapping)
    traces <- matrix(input$TraceMapping, ncol = 2, byrow = TRUE)
    indices <- as.integer(traces[traces[, 1] == input$TraceName, 2])
    plotlyProxy("MyPlot", session) %>%
      plotlyProxyInvoke("deleteTraces", indices)
  })
}


ui <- fluidPage(
  plotly_ui_mod("plotly_mod")
)

server <- function(input, output, session) {
  callModule(plotly_server_mod, "plotly_mod")
}

shinyApp(ui, server)

Previous Solution avoiding plotlyProxy:

I came here via this question.

You were explicitly asking for plotlyProxy() so I'm not sure if this is helpful to you, but here is a workaround to realize the expected behaviour via updating the data provided to plot_ly() instead of using plotlyProxy():

library(shiny)
library(plotly)

ui <- fluidPage(
  selectizeInput(inputId="myTraces", label="Trace names", choices = NULL, multiple = TRUE, options = list('plugins' = list('remove_button'), 'create' = TRUE, 'persist' = TRUE, placeholder = "...add or remove traces")),
  plotlyOutput("MyPlot")
)

server <- function(input, output, session){
  
  myData <- reactiveVal()
  
  observeEvent(input$myTraces, {
    tmpList <- list()
    
    for(myTrace in input$myTraces){
      tmpList[[myTrace]] <- data.frame(name = myTrace, x = rnorm(10),y = rnorm(10))
    }
    
    myData(do.call("rbind", tmpList))
    
    return(NULL)
  }, ignoreNULL = FALSE)
  
  output$MyPlot <- renderPlotly({
    if(is.null(myData())){
      plot_ly(type = "scatter", mode = "markers")
    } else {
      plot_ly(myData(), x = ~x, y = ~y, color = ~name, type = "scatter", mode = "markers") %>%
        layout(showlegend  = TRUE)
    }
  })
}

shinyApp(ui, server)