title: How to determine which plot is shown reactively
body: <p>Here are two plots I want to show in the APP. In ui.r, I have one input(plot type) and one output(plot).</p>
  
  <p>plot type input:</p>
  
  <pre><code>sidebarPanel(
               checkboxGroupInput("vo", 
                                  label = "Visualization Object", 
                                  choices = list("Polar Distance of VAR from nadir" = 1, 
                                                 "Real Value of VAR" = 2 
                                  ),
                                  selected = c(1,2)
               )
             )
  </code></pre>
  
  <p>and the plot output:</p>
  
  <pre><code>fluidRow(
             column(6,
                    plotOutput(outputId="polar", width = "600px", height = "600px")
             ),
             column(6,
                    plotOutput(outputId="paral", width = "600px", height = "600px")
             )
           )
  </code></pre>
  
  <p>In server.r, I use this:</p>
  
  <pre><code>if(1%in%vo){
    output$polar &lt;- renderPlot({
      # input$reset
  
      ap(whole_p[[ts$counter]])
    })}
    if(2%in%vo){
    output$paral &lt;- renderPlot({
      # input$reset
  
      av(whole_v[[ts$counter2]])
    })}
  </code></pre>
  
  <p>So how can I change the server code to make it work as: when I select <code>Polar Distance of VAR from nadir</code>, then only plot <code>output$polar</code> is shown in the ui, and when select <code>Real Value of VAR</code>, only plot <code>output$paral</code> is shown in the ui. Thanks.</p>