How to install development version of R packages github repository

Question

How can I install a package that is under development directly from a github repository and once installed how can I switch between development and CRAN versions?

The specific package I am interested in installing from git is ggplot2.

Answer 1

via Hadley at https://github.com/hadley/ggplot2

install.packages("devtools")

library(devtools)

dev_mode(on=T)

install_github("hadley/ggplot2")

# use dev ggplot2 now

# when finished do:

dev_mode(on=F)  #and you are back to having stable ggplot2