title: R shiny select variable based on checkboxGroupInput
body: <p>I am using R shiny to develop a interactive analysis tool. Now I want to do classification tree based on variables check in checkboxGroupInput. How can I select that subset of data? THX!</p>
  
  <p>UI:</p>
  
  <pre><code>       dateInput("date","Enter date:",value = date),
         checkboxGroupInput("variable", "Variable:",
                           choices = names ,selected = names
          )
  </code></pre>
  
  <p>server I tried, but doesn't work: </p>
  
  <pre><code> dataall &lt;-  reactive({
       filename &lt;- paste0("dataall_'", input$date, "'.RData")
       load(filename)
       feature.test[,names(feature.test) %in% input$variable]
     })
  </code></pre>
  
  <p>feature.test is data in loaded file.</p>