#
# Comment:
#
# Inspired by Figure 3.3 from 
# Wickham's book "ggplot2"
#

library(ggplot2)
print(
ggplot(data=ggplot2::mpg, aes(x=displ, y=hwy, shape=factor(cyl))) + 
    geom_point() +
    stat_smooth(method="lm", colour="black") +
    scale_shape_manual(values=c(1, 16, 3, 17)) + 
    theme_bw() 
)