title: Shiny Issue - Tracking User Settings in Multiuser Environment
body: <p>I asked this question on the Shiny user group, but haven't been able to get a response, so I'm posting it here as well.</p>
  
  <p>I have an app that needs to track a user's preference, with the possibility that several users may be using the app simultaneously.  For simplicity, let's say I have a list to contain a user's settings stored within the shiny server function. It's a long list (1000 elements) that contains attributes based on the user's interaction with the app. The user can in effect change any index of this list to one of hundreds of possible settings. My initial solution was something like this:</p>
  
  <pre><code>shinyServer(function(input, output, session) {
   settings &lt;&lt;- rep("A",1000)
  
   observe({
        input$changeSettingsButton
        settings[input$changeIndex] &lt;&lt;- input$newSetting
   })
  }
  </code></pre>
  
  <p>Which works great unless you have multiple people using the app at the same time, because the &lt;&lt;- creates a global, shared variable across sessions. Is there a good way to do this?</p>