title: Displaying an updated variable after clicking an action button in Shiny
body: <p>I'm new to shiny and trying to accomplish rather a simple task using an action button: </p>
  
  <ul>
  <li>User clicks a button and a function is called</li>
  <li>This function does some calculations using input variables and updates/creates several global variables (<code>reactiveValues</code>, probably inside an <code>observe</code> block?)</li>
  <li>I'd like to display those values back on the UI (using <code>render*</code> function)</li>
  <li>Whenever user changes input values, the UI is automatically updated</li>
  </ul>
  
  <p>Relevant code bits are:</p>
  
  <p><strong>server.R</strong></p>
  
  <pre><code>...
  rv &lt;- reactiveValues() 
  observe({
   if(input$run){
    rv$a &lt;- someFunc(input$aa)
   }
  })
  output$msg = renderText({ rv$a })
  ...
  </code></pre>
  
  <p><strong>ui.R</strong></p>
  
  <pre><code>...
  selectInput("aa", ...)
  ...
  actionButton("run", "Run")
  ...
  textOutput("msg")
  </code></pre>
  
  <p>How can I change <code>msg</code> based on the input <code>aa</code> each time user clicks the button?</p>