[shiny] selectinput interactive with sliderinput-2

ui：


library(shiny)

shinyUI((fluidPage(
   titlePanel("hirearchy data group"),
   sidebarLayout
   (
   sidebarPanel
   (
   selectInput("brand",label="choice the brand",choices=c("all","w","s")),
   sliderInput("amount",label="choice the amount",min=range(df$amount)[1],max=range(df$amount)[2],value=0)

   ),

   mainPanel
   (
   dataTableOutput("table")
   )

   ))))

server：

library(shiny)

## test dataframe
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(10,9,7,8,6,4,7,3,2,1))
df$id=as.character(df$id)
df$brand=as.character(df$brand)
df$model=as.character(df$model)


shinyServer(function(input, output, session) {
   output$table <- renderDataTable({
      if(input$brand!="all") {df=df[which(df$brand==input$brand),]}
      if(input$amount!=0) {df=df[which(df$amount==input$amount),]}

   df
   })
   amount=observe(
      {
      input$brand
         if (input$brand=="all"){val=range(df$amount)}
         else if (input$brand=="w"){val=range(df$amount[df$brand==input$brand])}
         else if (input$brand=="s"){val=range(df$amount[df$brand==input$brand])}
         updateSliderInput(session,"amount",min=val[1],max=val[2],value=val[1])
      }
   )
})