function to automate repeated groups of UI elements

server.R

library(shiny)

items <- c("seed")

shinyServer(function(input, output) {

  # closure to generate reactive function to add items
  cl_add_item <- function(name_value, name_button){
    
    # function to add item
    add_item <- reactive({
      
      # register button
      n_click <- input[[name_button]]
      
      if (n_click > 0){
        # get the (isolated) value of the UI element
        new_item <- isolate(input[[name_value]])
        # add it to the global vector
        items <<- c(items, new_item)
      }
      
      # no need to return anything
      return()
      
    })
    
    # return the "completed" function
    return(add_item)
    
  }
  
  add_item_a <- cl_add_item("item_add_a", "item_add_a_go")
  add_item_b <- cl_add_item("item_add_b", "item_add_b_go")
      
  get_items <- reactive({
    
    # register "adders"
    add_item_a()
    add_item_b()
    
    # return the global vector
    return(items)
    
  })

  # print out the contents of global vector
  output$show_items <- renderPrint(get_items())
  
})

ui.R

library(shiny)

text_button <- function(inputId_text, inputId_button, 
                        label_text="", value_text="", label_button="Go!"){
  
  text <- textInput(inputId=inputId_text, label=label_text, value=value_text)
  button <- actionButton(inputId=inputId_button, label=label_button)
  
  return(list(text, button))
  
}

shinyUI(pageWithSidebar(
  
  # Application title
  headerPanel("Test of reactivity and closures, combining UI elements"),
    
  sidebarPanel(
 
    text_button(inputId_text="item_add_a", inputId_button="item_add_a_go",
                label_text="Add an item here", value_text=""),
    text_button(inputId_text="item_add_b", inputId_button="item_add_b_go",
                label_text="Or, add an item here", value_text="")
    
  ),
  
  mainPanel(
  
    verbatimTextOutput(outputId="show_items")
    
  )
  
))