title: How to access a column of a DataFrame from a passed variable in Shiny?
body: <p>I'm trying to create a simple shiny app where the user can select a variable from a drop down menu and then a plot is generated. The selected variable is seen as input$Feature w/in the server function but I am getting errors when trying to access the column of my data frame as df$input$Feature. I'm not sure how to do this.</p>
  
  <pre><code>bw &lt;- read.xls('filename')
  
  ui &lt;- fluidPage(
    selectInput(inputId = 'Feature',
                 label = 'Select a feature to plot:',
                 c(colnames(bw))),
    plotOutput('graph')
  )
  
  server &lt;- function(input, output){
    output$graph &lt;- renderPlot({
      p &lt;- ggplot(bw, aes(bw$Date))
      p &lt;- p + geom_line(aes(y=bw$input$Feature, colour='red', group=1))
      p &lt;- p + labs(x = 'Date', y = 'Feature Name')
      print(p)
    })
  }
  
  shinyApp(ui=ui, server=server)
  </code></pre>