如何根据用户输入在Shiny中对棒棒糖图表中的数据进行排序？

library(shiny)
library(ggplot2)

# 定义数据
data <- data.frame(
  Category = c("A", "B", "C", "D"),
  Value = c(10, 20, 30, 40)
)

# 定义UI
ui <- fluidPage(
  titlePanel("排序棒棒糖图表"),
  sidebarLayout(
    sidebarPanel(
      selectInput("sort_by", "排序方式", choices = c("按数值升序", "按数值降序"))
    ),
    mainPanel(
      plotOutput("lollipop_plot")
    )
  )
)

# 定义Server函数
server <- function(input, output) {
  # 根据用户选择的排序方式对数据进行排序
  sorted_data <- reactive({
    if (input$sort_by == "按数值升序") {
      data <- data[order(data$Value), ]
    } else if (input$sort_by == "按数值降序") {
      data <- data[order(-data$Value), ]
    }
    data
  })
  
  # 绘制棒棒糖图表
  output$lollipop_plot <- renderPlot({
    ggplot(sorted_data(), aes(x = Category, y = Value)) +
      geom_segment(aes(xend = Category, yend = 0), color = "gray") +
      geom_point(size = 3) +
      geom_text(aes(label = Value), vjust = -0.5) +
      coord_flip() +
      labs(x = "类别", y = "数值", title = "排序棒棒糖图表")
  })
}

# 运行Shiny应用程序
shinyApp(ui, server)