How to add/remove input fields dynamically by a button in shiny

Question

I've been trying to find a solution how to add and remove input fields with a button in shiny. I don't have a source code since I haven't made that much progress, but this jQuery example (http://www.mkyong.com/jquery/how-to-add-remove-textbox-dynamically-with-jquery/) gives a good idea on what I'm trying to accomplish. Is this possible in shiny or should I use shinyjs to do this? Thank you in advance!

Answer 1

EDIT: I read the jQuery example a bit more, and added a code snippet doing what I think you were looking for.

I don't know jQuery, so I couldn't make much out of the example link. I took a guess on what you wanted, but I think the key idea is the use of renderUI and uiOutput even if my suggestion here misses the point.

To toggle a ui element:

If you specifically don't want to use shinyjs, you could do something like this:

library(shiny)

ui <- shinyUI(fluidPage(

  actionButton("btn", "Toggle Textbox"),

  textOutput("btn_val"),
  uiOutput("textbox_ui")

))

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

  output$btn_val <- renderPrint(print(input$btn))

  textboxToggle <- reactive({

    if (input$btn %% 2 == 1) {
      textInput("textin", "Write something:", value = "Hello World!")
    }

  })

  output$textbox_ui <- renderUI({ textboxToggle() })

})

shinyApp(ui, server)

To add and remove elements:

After reading a bit of the jQuery example, I think this is similar to what you were looking for:

library(shiny)

ui <- shinyUI(fluidPage(

  sidebarPanel(

      actionButton("add_btn", "Add Textbox"),
      actionButton("rm_btn", "Remove Textbox"),
      textOutput("counter")

    ),

  mainPanel(uiOutput("textbox_ui"))

))

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

  # Track the number of input boxes to render
  counter <- reactiveValues(n = 0)

  observeEvent(input$add_btn, {counter$n <- counter$n + 1})
  observeEvent(input$rm_btn, {
    if (counter$n > 0) counter$n <- counter$n - 1
  })

  output$counter <- renderPrint(print(counter$n))

  textboxes <- reactive({

    n <- counter$n

    if (n > 0) {
      lapply(seq_len(n), function(i) {
        textInput(inputId = paste0("textin", i),
                  label = paste0("Textbox", i), value = "Hello World!")
      })
    }

  })

  output$textbox_ui <- renderUI({ textboxes() })

})

shinyApp(ui, server)

The problem with this approach is that each time you press the add or remove button, all of the input boxes get re-rendered. This means that any input you might have had on them disappears.

I think you could get around that by also saving the current input values of the input boxes into a reactiveValues object, and setting the values from the object as the starting values of the re-rendered input boxes by using the value option in textInput. I'll leave the implementation of that for now, though.