Shiny renderUI with multiple inputs

Question

My Shiny App has multiple inputs that depend on the number of variables used. A simplified version, though not working, is below. I was able to get the UI to update based upon the numericInput using a function called Make.UI which I used to make uiOutput, but getting the inputs back into the server is beyond my Shiny skill set! Any suggestions would be greatly appreciated.

gwynn

library(shiny)
D = matrix(runif(400), nrow = 20)
colnames(D) = labs = sapply(1:20, function(i) {paste0("col",i)})

# Define UI for application that summarises data
ui <- fluidPage(

  # Application title
  titlePanel("Summaries"),

  # Select columns to get fed into summary 
  tabsetPanel(
    tabPanel("Matching Variables Info",
             sidebarPanel(

               numericInput("NoVars","No. of variables to summarize", 
                            value = 3, min = 2, max = dim(D)[2]),

               uiOutput("VarsInput")
             ),

             # Show summaries of columns choosen above
             mainPanel(
               verbatimTextOutput("dataInfo")
             )
    )
  )
)


# Define the server code
server <- function(input, output){

  Make.UI <- function(NoV){
    C = sapply(1:NoV, function(i){paste0("cols",i)})
    L = sapply(1:NoV, function(i){paste0("label",i)})

    output = tagList()

    for(i in seq_along(1:NoV)){
      output[[i]] = tagList()
      output[[i]][[1]] = selectInput(C[i], "Variable to summarize:", labs)
      output[[i]][[2]] = textInput(L[i], label = "Label for variable:", 
                                   value = "Label for variable Here")
    } ## for loop

    output
  } # closes Make.UI function

  K <- reactive({
    input$NoVars
  })

  output$VarsInput <- renderUI({
    Make.UI(K())
  })

  output$dataInfo <- renderPrint({
    C <- sapply(1:K(), function(i) {input[[paste0("cols",i)]]})
    ## the code in the line above doesn't work

    summary(D[, C()])
  })

}

# Return a Shiny app object
shinyApp(ui = ui, server = server)

Answer 1

Like I wrote in the first comment, I am unsure about the Make.UI()function. If you really want to keep it as a seperate function you should make it reactive. Or just use it as I did in the code below. Moreover, in output$dataInfo <- renderPrint({ C is not a reactive() function so you would need to remove brackets there.

library(shiny)
D = matrix(runif(400), nrow = 20)
colnames(D) = labs = sapply(1:20, function(i) {paste0("col",i)})

# Define UI for application that summarises data
ui <- fluidPage(
  
  # Application title
  titlePanel("Summaries"),
  
  # Select columns to get fed into summary 
  tabsetPanel(
    tabPanel("Matching Variables Info",
             sidebarPanel(
               
               numericInput("NoVars","No. of variables to summarize", 
                            value = 3, min = 2, max = dim(D)[2]),
               
               uiOutput("VarsInput")
             ),
             
             # Show summaries of columns choosen above
             mainPanel(
               verbatimTextOutput("dataInfo")
             )
    )
  )
)


# Define the server code
server <- function(input, output){
  
  K <- reactive({
    input$NoVars
  })
  
  output$VarsInput <- renderUI({
    NoV = K()
    C = sapply(1:NoV, function(i){paste0("cols",i)})
    L = sapply(1:NoV, function(i){paste0("label",i)})
    
    output = tagList()
    
    for(i in seq_along(1:NoV)){
      output[[i]] = tagList()
      output[[i]][[1]] = selectInput(C[i], "Variable to summarize:", labs)
      output[[i]][[2]] = textInput(L[i], label = "Label for variable:", 
                                   value = "Label for variable Here")
    }
    
    output
  })
  
  output$dataInfo <- renderPrint({
    C <- sapply(1:K(), function(i) {input[[paste0("cols",i)]]})
    ## the code in the line above doesn't work
    
    summary(D[, C])
  })
  
}

# Return a Shiny app object
shinyApp(ui = ui, server = server)