The abline() function is a base R function that allows you to add a straight line to an existing plot. You can specify the slope and intercept of the line, or use a linear model object as an argument.

ggplot2 is not only the R language’s most popular data visualization package, it is also an ecosystem. Numerous add-on packages give ggplot added power to do everything from more easily changing ...

Note that you need at least version 0.4.0 of the rlang package for this to work. At the time I wrote this article, version 0.4.0 was on CRAN but you needed to compile it from source when given ...