How can I add a diagonal line to my scatter plot?

Question

R

To add a diagonal line to a scatter plot you can use:

1) addline(diag)
2) abline(0,1)
3) geom_line=(diag)
4) line(1,1)

And if you don't mind, could you write code that can serve as an example.

Answer 1

plot(c(-2,-1,0,1,2), c(-2,-1,0,1,2))
abline(0,1)