server.r

data_sets <- c("mtcars", "morley", "rock")

shinyServer(function(input, output) {

  # Drop-down selection box for which data set
  output$choose_dataset <- reactiveUI(function() {
    selectInput("dataset", "Data set", as.list(data_sets))
  })

  # Check boxes
  output$choose_columns <- reactiveUI(function() {
    # If missing input, return to avoid error later in function
    if(is.null(input$dataset))
      return()

    # Get the data set with the appropriate name
    dat <- get(input$dataset)
    colnames <- names(dat)

    # Create the checkboxes and select them all by default
    checkboxGroupInput("columns", "Choose columns", 
                        choices  = colnames,
                        selected = colnames)
  })


  # Output the data
  output$data_table <- reactiveTable(function() {
    options(shiny.table.class = "table table-striped");
    # If missing input, return to avoid error later in function
    if(is.null(input$dataset))
      return()

    # Get the data set
    dat <- get(input$dataset)

    # Make sure columns are correct for data set (when data set changes, the
    # columns will initially be for the previous data set)
    if (is.null(input$columns) || !(input$columns %in% names(dat)))
      return()

    # Keep the selected columns
    dat <- dat[, input$columns, drop = FALSE]

    # Return first 20 rows
    head(dat, 20)
  })
})

ui.r

shinyUI(pageWithSidebar(

  headerPanel(""),

  sidebarPanel(
    uiOutput("choose_dataset"),

    uiOutput("choose_columns")
  ),


  mainPanel(
    tableOutput("data_table")
  )
))