How to limit the number of options a user can select with selectInput in R shiny when multiple is tr-CodePudding

I have a Shiny app, and I want users to be able to select multiple options--but only up to a certain limit. I can't find a way to limit the numbers.

Below is a simple, reproducible example. In it, I was users to only be able to select up to 2/4 options for the first question, up to 3/4 for the second, and as many as they'd like for the third question (no edits needed for question 3).

library(shiny)

ui <- fluidPage(
  
  
  sidebarLayout(
    sidebarPanel(                     selectInput("q1", label = "Choose up to 2.", choices = c(" ", "option 1", "option 2", "option 3", "option 4"), multiple = TRUE),
                                      selectInput("q2", label = "Choose up to 3.", choices = c(" ", "option 1", "option 2", "option 3", "option 4"), multiple = TRUE),
                                      selectInput("q3", label = "Choose as many as you want.", choices = c(" ", "option 1", "option 2", "option 3", "option 4"), multiple = TRUE)),
    mainPanel(
  
    )
  )
)

server <- function(input, output) {
  
  
}

# Run the application 
shinyApp(ui = ui, server = server)

CodePudding user response：

Instead of selectInput you can use selectizeInput and use the options argument to set the maximum allowed items using maxItems.

library(shiny)

ui <- fluidPage(sidebarLayout(
  sidebarPanel(
    selectizeInput(
      "q1",
      label = "Choose up to 2.",
      choices = c(" ", "option 1", "option 2", "option 3", "option 4"),
      multiple = TRUE,
      options = list(maxItems = 2)
    ),
    selectizeInput(
      "q2",
      label = "Choose up to 3.",
      choices = c(" ", "option 1", "option 2", "option 3", "option 4"),
      multiple = TRUE,
      options = list(maxItems = 3)
    ),
    selectInput(
      "q3",
      label = "Choose as many as you want.",
      choices = c(" ", "option 1", "option 2", "option 3", "option 4"),
      multiple = TRUE
    )
  ),
  mainPanel()
))

server <- function(input, output) {
  
}

# Run the application
shinyApp(ui = ui, server = server)