checkboxGroupInput - set minimum and maximum number of selections - ticks

Question

Here is example code with check-box group input:

library(shiny)

server <- function(input, output) {
  output$Selected <- renderText({
    paste(input$Sele         


        

Answer 1

You can do something like this:

library(shiny)

my_min <- 1
my_max <- 3

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      checkboxGroupInput("SelecetedVars", "MyList:",paste0("a",1:5), selected = "a1")
    ),
    mainPanel(textOutput("Selected"))
  )
)

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

  output$Selected <- renderText({
    paste(input$SelecetedVars,collapse=",")
  })

  observe({
    if(length(input$SelecetedVars) > my_max){
      updateCheckboxGroupInput(session, "SelecetedVars", selected= tail(input$SelecetedVars,my_max))
    }
    if(length(input$SelecetedVars) < my_min){
      updateCheckboxGroupInput(session, "SelecetedVars", selected= "a1")
    }
  })
}

shinyApp(ui = ui, server = server)