Further reading
Additional examples can be found on the respective help pages of each geometric attribute, or on the webpages of the ggplot
document. Here are some useful links to such pages:
The qplot function: http://docs.ggplot2.org/current/qplot.html
Histograms: http://docs.ggplot2.org/current/geom_histogram.html
Density plots: http://docs.ggplot2.org/current/geom_density.html and http://docs.ggplot2.org/current/stat_density.html
Bar charts: http://docs.ggplot2.org/current/geom_bar.html
Scatterplots and Bubble charts: http://docs.ggplot2.org/0.9.3.1/geom_point.html