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.

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 ...

Learn how to make everything from basic line graphs to racing bar charts — all interactive and easily animated — with the echarts4r R package.