dplyr
- https://github.com/rstudio/cheatsheets/raw/master/source/pdfs/data-transformation-cheatsheet.pdf
- https://www.rstudio.com/wp-content/uploads/2015/02/data-wrangling-cheatsheet.pdf
ggplot2
R markdown
- https://www.rstudio.com/wp-content/uploads/2016/03/rmarkdown-cheatsheet-2.0.pdf
- https://www.rstudio.com/wp-content/uploads/2015/03/rmarkdown-reference.pdf