title: How to format number values for ggplot2 legend?
body: <p>I am working on finishing up a graph generated using ggplot2 like so...</p>
  
  <pre><code>ggplot(timeSeries, aes(x=Date, y=Unique.Visitors, colour=Revenue)) 
  + geom_point() + stat_smooth() + scale_y_continuous(formatter=comma)
  </code></pre>
  
  <p>I have attached the result and you can see the numeric values in the legend for Revenue do not have a comma. How can I add a comma to those values? I was able to use scale_y_continuous for the axis, can that be used for the legend also?</p>
  
  <p><img src="https://i.stack.imgur.com/hZ7c0.jpg" alt="alt text"></p>