shiny interactive select

library(shiny)
df <- data.frame(id = c("1","1","1","1","1","1","2","2","2","2"),
                 brand = c("w","w","w","s","s","s","w","w","w","s"),
                 model =
c("w123","w123","w456","s99","s88","s88","w123","w456","w456","s99"),
                 amount = c(10,9,7,8,6,4,7,3,2,8))
df$id=as.character(df$id)
df$brand=as.character(df$brand)
df$model=as.character(df$model)
app = shinyApp(
  ui = shinyUI(fluidPage(
   titlePanel("hirearchy data group"),
   sidebarLayout
   (
   sidebarPanel
   (
   selectInput("brand",label="choice the brand",choices=c("all","w","s")),
   selectInput("model",label="choice the model",choices=c("all","w123","w456","s99","s88"))
   ),
   mainPanel
   (
   dataTableOutput("table")
   )
   ))),
  server = function(input, output, session) {
    output$table <- renderDataTable({
      if(input$brand!="all") {df=df[which(df$brand==input$brand),]}
      if(input$model!="all") {df=df[which(df$model==input$model),]}
    df
    })
    models = observe({
      input$brand
      if (input$brand=="all"){
        choice = c("all", unique(df$model))
      }else{
        choice = c("all", unique(df[df$brand==input$brand,]$model))
      }
      updateSelectInput(session, "model", choice = choice)
    })
  }
)
runApp(app)