Literaturverzeichnis

Wickham, Hadley. 2009. Ggplot2: Elegant Graphics for Data Analysis. New York: Springer Science & Business Media.

Xie, Yihui. 2015. Dynamic Documents with R and Knitr. 2nd ed. Boca Raton, Florida: Chapman; Hall/CRC. http://yihui.org/knitr/.