Exercise 1.1: Scatterplot

ggplot(crampton.pig, aes(weight1, weight2, color = treatment, size = feed)) + 
  geom_point()

Exercise 1.2: Tile plot

ggplot(crampton.pig, aes(rep, treatment, fill = weight2 - weight1)) + 
  geom_tile(color = "black", size = 2)