如何用几行代码实现R.shiny多层次的selectInput

library(shiny)

ui <- fluidPage(
  selectizeInput(inputId = "level1", label = "Level 1", choices = NULL),
  selectizeInput(inputId = "level2", label = "Level 2", choices = NULL),
  selectizeInput(inputId = "level3", label = "Level 3", choices = NULL)
)

server <- function(input, output, session) {
  observeEvent(input$level1, {
    # 根据Level 1的选择更新Level 2的选项
    level2_choices <- get_level2_choices(input$level1)
    updateSelectizeInput(session, "level2", choices = level2_choices)
  })
  
  observeEvent(input$level2, {
    # 根据Level 2的选择更新Level 3的选项
    level3_choices <- get_level3_choices(input$level2)
    updateSelectizeInput(session, "level3", choices = level3_choices)
  })
  
  # 模拟获取Level 2的选项
  get_level2_choices <- function(level1) {
    # 根据Level 1的选择返回对应的Level 2选项
    # 这里可以根据实际需求进行数据处理和筛选
    if (level1 == "Option 1") {
      return(c("Option 1-1", "Option 1-2", "Option 1-3"))
    } else if (level1 == "Option 2") {
      return(c("Option 2-1", "Option 2-2"))
    } else {
      return(NULL)
    }
  }
  
  # 模拟获取Level 3的选项
  get_level3_choices <- function(level2) {
    # 根据Level 2的选择返回对应的Level 3选项
    # 这里可以根据实际需求进行数据处理和筛选
    if (level2 == "Option 1-1") {
      return(c("Option 1-1-1", "Option 1-1-2"))
    } else if (level2 == "Option 1-2") {
      return(c("Option 1-2-1", "Option 1-2-2", "Option 1-2-3"))
    } else {
      return(NULL)
    }
  }
}

shinyApp(ui, server)