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

are you looking for something like this?

library(shiny)


LHSchoices <- c("X1", "X2", "X3", "X4")


#------------------------------------------------------------------------------#

# MODULE UI ----
variablesUI <- function(id, number) {

  ns <- NS(id)

  tagList(
    fluidRow(
      column(6,
             selectInput(ns("variable"),
                         paste0("Select Variable ", number),
                         choices = c("Choose" = "", LHSchoices)
             )
      ),

      column(6,
             numericInput(ns("value.variable"),
                          label = paste0("Value ", number),
                          value = 0, min = 0
             )
      )
    )
  )

}

#------------------------------------------------------------------------------#

# MODULE SERVER ----

variables <- function(input, output, session, variable.number){
  reactive({

    req(input$variable, input$value.variable)

    # Create Pair: variable and its value
    df <- data.frame(
      "variable.number" = variable.number,
      "variable" = input$variable,
      "value" = input$value.variable,
      stringsAsFactors = FALSE
    )

    return(df)

  })
}

#------------------------------------------------------------------------------#

# Shiny UI ----

ui <- fixedPage(
  verbatimTextOutput("test1"),
  tableOutput("test2"),
  variablesUI("var1", 1),
  h5(""),
  actionButton("insertBtn", "Add another line")

)

# Shiny Server ----

server <- function(input, output) {

  add.variable <- reactiveValues()

  add.variable$df <- data.frame("variable.number" = numeric(0),
                                "variable" = character(0),
                                "value" = numeric(0),
                                stringsAsFactors = FALSE)

  var1 <- callModule(variables, paste0("var", 1), 1)

  observe(add.variable$df[1, ] <- var1())

  observeEvent(input$insertBtn, {

    btn <- sum(input$insertBtn, 1)

    insertUI(
      selector = "h5",
      where = "beforeEnd",
      ui = tagList(
        variablesUI(paste0("var", btn), btn)
      )
    )

    newline <- callModule(variables, paste0("var", btn), btn)

    observeEvent(newline(), {
      add.variable$df[btn, ] <- newline()
    })

  })

  output$test1 <- renderPrint({
    print(add.variable$df)
  })

  output$test2 <- renderTable({
    add.variable$df
  })

}

#------------------------------------------------------------------------------#

shinyApp(ui, server)