ggplot line
http://www.sthda.com/english/wiki/ggplot2-add-straight-lines-to-a-plot-horizontal-vertical-and-regression-lines
mtcars %>% ggplot(aes(x=wt, y=mpg)) + geom_point() + geom_hline(yintercept=15) + geom_vline(xintercept=2) + geom_abline(intercept=37, slope=-5, linetype="dashed", color="red", size=3)+ stat_smooth(method="lm", se=F) + geom_segment(aes(x=3, y=15, xend=4, yend=25), arrow=arrow(length=unit(5,"mm")), color="pink")
![](https://onesixx.com/wp-content/uploads/2020/07/image-3.png)
mtcars %>% ggplot(aes(x=wt, y=mpg)) + geom_point() + \tgeom_hline(data=mtcars, aes(yintercept=cyl))