shiny dynamically add input fields and data without getting re-rendered

Question

I'm trying to dynamically add new variables to my shiny app which is working but if I start editing one, the values (text and numeric) reset each time I then add an additional variable. This example works without needing a for loop using reactiveValuesToList() but when I apply it to my code, it doesn't work. Here is my working example:

library(shiny)
dist <- c("Normal", "Gamma")
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)

  # Track all user inputs
  AllInputs <- reactive({
    x <- reactiveValuesToList(input)
  })

  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) {
      isolate({
        lapply(seq_len(n), function(i) {
        fluidRow(
          selectInput(inputId = paste0("news", i),
                      label = paste0("Variable ", i),
                      choices = dist),

          conditionalPanel(
            condition = sprintf("input.%s=='Normal'", paste0("news", i)),
            textInput("txt", "Text input:", paste0("var", i)),  
            column(width = 3, numericInput('normal_mean', 'Mean', value = '0')), column(width = 3, numericInput('normal_sd', 'Standard deviation', value = '1'))),

          conditionalPanel(
            condition =  sprintf("input.%s=='Gamma'", paste0("news", i)),
            textInput("txt", "Text input:", paste0("var", i)),
            column(width = 3, numericInput('gamma_shape', 'Shape', value = '0')), column(width = 3, numericInput('gamma_scale', 'Scale', value = '1')))
        )
        })
      })
    }

  })

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

})

shinyApp(ui, server)

Now if I try and add AllInputs()[[]] to textInput it doesn't keep the text in the conditionalPanel call:

conditionalPanel(
            condition = sprintf("input.%s=='Normal'", paste0("news", i)),
            textInput("txt", "Text input:", AllInputs()[[paste0("var", i)]]),  
            column(width = 3, numericInput('normal_mean', 'Mean', value = '0')), column(width = 3, numericInput('normal_sd', 'Standard deviation', value = '1')))

I'm also not sure how to include AllInputs()[[]] to the numeric values so that they dont change.

I think the problem is because of my condition line within conditionalPanel but can't figure it out, any suggestions? thanks

bretauv · Accepted Answer · 2020-03-23T21:59:53.543

You should consider using modules and insertUI / removeUI. Clicking on the buttons will not reset your changes on the inputs you already called. Here, you just have inputs so you only need to call the function add_box I created, but if you want to add outputs in the module, then you will need to use the function callModule in observeEvent. This is explained in the article I refer to.

This is not the method you suggested but it works.

library(shiny)

dist <- c("Normal", "Gamma")

add_box <- function(id){
  ns <- NS(id)
  tags$div(id = paste0("new_box", id),
           selectInput(inputId = ns("news"),
                       label = paste0("Variable ", id),
                       choices = dist),

           conditionalPanel(
             condition = "input.news=='Normal'",
             ns = ns,
             textInput(ns("txt"), "Text input:", paste0("var", id)),  
             column(width = 3, numericInput(ns('normal_mean'), 'Mean', value = '0')), 
             column(width = 3, numericInput(ns('normal_sd'), 'Standard deviation', value = '1'))),

           conditionalPanel(
             condition =  "input.news=='Gamma'",
             ns = ns,
             textInput(ns("txt"), "Text input:", paste0("var", id)),
             column(width = 3, numericInput(ns('gamma_shape'), 'Shape', value = '0')), 
             column(width = 3, numericInput(ns('gamma_scale'), 'Scale', value = '1')))
  )
}


ui <- shinyUI(fluidPage(

  sidebarPanel(

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

  ),

  mainPanel(column(width = 12, id = "column"))

))

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

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

  # Track all user inputs
  AllInputs <- reactive({
    x <- reactiveValuesToList(input)
  })

  observeEvent(input$add_btn, {
    counter$n <- counter$n + 1
    insertUI(selector = "#column",
             where = "beforeEnd",
             ui = add_box(counter$n)
    )
  })

  observeEvent(input$rm_btn, {
    if (counter$n > 0) {
      removeUI(selector = paste0("#new_box", counter$n))
      counter$n <- counter$n - 1
    }
  })

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


})

shinyApp(ui, server)

thanks, i must read into modules. The output at the moment isn't correct though as when you click "add textbox", both gamma and normal available even though only "normal" is chosen? — user63230, Mar 23 '20 at 21:42
oh, I didn't notice this feature in your example. I will try to adapt my answer — bretauv, Mar 23 '20 at 21:47
@user63230 it's corrected, I slightly changed the condition and added `ns = ns` in each `conditionalPanel` — bretauv, Mar 23 '20 at 22:00

shiny dynamically add input fields and data without getting re-rendered

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