在Shiny中，如果所选变量是数值变量，如何输出直方图；如果变量是分类变量，如何输出条形图？

library(shiny)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      selectInput("variable", "选择变量：", choices = colnames(mtcars))
    ),
    mainPanel(
      plotOutput("histogram")
    )
  )
)

server <- function(input, output) {
  output$histogram <- renderPlot({
    data <- mtcars[[input$variable]]
    hist(data, main = "直方图", xlab = input$variable, col = "blue")
  })
}

shinyApp(ui, server)

library(shiny)

ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      selectInput("variable", "选择变量：", choices = colnames(iris)[-5])
    ),
    mainPanel(
      plotOutput("barchart")
    )
  )
)

server <- function(input, output) {
  output$barchart <- renderPlot({
    data <- iris[[input$variable]]
    counts <- table(data)
    barplot(counts, main = "条形图", xlab = input$variable, col = "orange")
  })
}

shinyApp(ui, server)