R Shiny: How to dynamically append arbitrary number of input widgets

Question

The goal

I am working on a Shiny app that allows the user to upload their own data and focus on the entire data or a subset by providing data filtering widgets describ

Answer 1

You need to check for existing input values and use them if available:

  # Prevent dynamic inputs from resetting
  newInputValue <- "Option 1"
  if (newInputId %in% names(input)) {
    newInputValue <- input[[newInputId]]
  }
  # Define new input
  newInput <- selectInput(newInputId, newInputLabel, c("Option 1", "Option 2", "Option 3"), selected=newInputValue)

A working version of the gist (without the reset problem) can be found here: https://gist.github.com/motin/0d0ed0d98fb423dbcb95c2760cda3a30

Copied below:

ui.R

library(shiny)

shinyUI(pageWithSidebar(

  # Application title
  headerPanel("Dynamically append arbitrary number of inputs"),

  # Sidebar with a slider input for number of bins
  sidebarPanel(
    uiOutput("allInputs"),
    actionButton("appendInput", "Append Input")
  ),

  # Show a plot of the generated distribution
  mainPanel(
    p("This shows how to add an arbitrary number of inputs
      without resetting the values of existing inputs each time a new input is added.
      For example, add a new input, set the new input's value to Option 2, then add
      another input. Note that the value of the first input does not reset to Option 1.")
  )
))

server.R

library(shiny)

shinyServer(function(input, output) {

  output$allInputs <- renderUI({
    # Get value of button, which represents number of times pressed (i.e. number of inputs added)
    inputsToShow <- input$appendInput
    # Return if button not pressed yet
    if(is.null(inputsToShow) || inputsToShow < 1) return()
    # Initialize list of inputs
    inputTagList <- tagList()
    # Populate the list of inputs
    lapply(1:inputsToShow,function(i){
      # Define unique input id and label
      newInputId <- paste0("input", i)
      newInputLabel <- paste("Input", i)
      # Prevent dynamic inputs from resetting
      newInputValue <- "Option 1"
      if (newInputId %in% names(input)) {
        newInputValue <- input[[newInputId]]
      }
      # Define new input
      newInput <- selectInput(newInputId, newInputLabel, c("Option 1", "Option 2", "Option 3"), selected=newInputValue)
      # Append new input to list of existing inputs
      inputTagList <<- tagAppendChild(inputTagList, newInput)
    })
    # Return updated list of inputs
    inputTagList
  })

})

(The solution was guided on Nick's hints in the original gist from where you got the code of the promising solution)