Shiny R：如何评估数据集名称以打印数据集

Question

我想在R闪亮的网页应用中打印数据集值。但是下面的代码是在UI输出中打印数据集的名称。如何打印数据集的值？

library(MASS)
library(shinythemes)
library(shiny)
library(ggplot2)

mass.tmp <- data(package = "MASS")[3]
mass.datasets <- as.vector(mass.tmp$results[,3])

ui <- fluidPage(

  theme = shinytheme("superhero"),
  titlePanel("Linear Regression Modelling"),
  sidebarLayout(
    sidebarPanel(
      selectInput("dsname", "Dataset:",choices = c(mass.datasets))
      ,
       uiOutput("x_axis")
      ,
       tableOutput("tab")
    ),
    mainPanel(
      tags$br(),
      tags$br()
  )
)
)

server <- function(input, output) {

  num_ds <- function(ds)
  {
    nums <- sapply(ds,is.numeric)
    num_ds <- ds[,nums]
    return(num_ds)
  }

  ds_ext <- reactive({  num_ds(input$dsname) })

  output$tab <- renderTable({  eval(input$dsname) })

    # output$x_axis <- renderUI({
    #    col_opts <- get(ds_ext())
    #    selectInput("x_axis2", "Independent Variable:", choices = names(col_opts))
    # })

}

shinyApp(ui = ui, server = server)

这是完整的代码。我正在尝试显示MASS包中的数据集，如上面的代码所示。