title: Annotate ggplot bar plot in R
body: <p>How can I annotate the following plot? I want to include counts on top of each bar.</p>
  <pre><code>g &lt;- ggplot(mpg, aes(class))
  # Number of cars in each class:
  g + geom_bar()
  </code></pre>
  <p>I only know how to do it if I do a group by and create a new column 'count' for example.</p>