title: Thousand separator in label of x or y axis
body: <p>I would like to have pretty labels on the y-axis. For example, I prefer to have 1,000 instead of 1000. How can I perform this in ggplot? Here is a minimum example:</p>
  
  <pre><code>x &lt;- data.frame(a=c("a","b","c","d"), b=c(300,1000,2000,4000))
  ggplot(x,aes(x=a, y=b))+
                 geom_point(size=4)
  </code></pre>
  
  <p>Thanks for any hint.</p>