title: How to format R Shiny numericInput?
body: <p>I have a Shiny app with numerous <code>numericInput</code> fields.  I would like a way to format the <code>numericInput</code> fields with commas separating every 10^3.  For example, I want 5,000,000 instead of 5000000.</p>
  
  <p>I can do this in R with the <code>format</code> and <code>prettyNum</code> functions. But I don't have a way to do this in Shiny.</p>
  
  <p>This would be very helpful for the UI because it would work with percents, money, etc.  Does anyone have any idea how to incorporate this into the <code>numericInput</code> field?</p>
  
  <p>Thanks!</p>
  
  <pre><code>library(shiny)
  
  # Define UI for application that draws a histogram
  ui &lt;- fluidPage(
    mainPanel(
      numericInput("formatNumber",
                   "Number should be formatted, e.g."5,000,000",
                   value = 1000),
      p(format(5000000.10, big.mark=",", big.interval=3L,
               digits=0, scientific=F))
    )
  )
  
  server &lt;- function(input, output) {  
  }
  
  shinyApp(ui = ui, server = server)
  </code></pre>