当 multiple 为 true 时，如何限制用户可以使用 R闪亮的 selectInput 选择的选项数量？

Question

我有一个 Shiny 应用程序，我希望用户能够选择多个选项，但仅限于一定的限制。我找不到限制数量的方法。

下面是一个简单的、可重现的示例。在其中，我的用户只能为第一个问题选择最多 2/4 个选项，为第二个问题选择最多 3/4 个选项，为第三个问题选择任意数量的选项（问题无需编辑） 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)

Answer 1

您可以使用 selectizeInput 代替 selectInput 并使用options参数来设置允许的最大项目数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)