<pre>
> d <- ggplot(diamonds, aes(x = cut, y = clarity, group = 1))
> d + stat_sum()
<a href='web/graphics/8587c5702fb3acb73a413eea34467072.pdf'><img src='web/graphics/8587c5702fb3acb73a413eea34467072.png' /></a>

> qplot(cut, clarity, data = diamonds)
<a href='web/graphics/53434821c82fc48de10318716c0d2b1e.pdf'><img src='web/graphics/53434821c82fc48de10318716c0d2b1e.png' /></a>

> qplot(cut, clarity, data = diamonds, stat = "sum")
<a href='web/graphics/2cb57dae1f2fcf2bf1289c51518573a4.pdf'><img src='web/graphics/2cb57dae1f2fcf2bf1289c51518573a4.png' /></a>

</pre>
