R - create secondary axis in ggplot2

library(ggplot2)
p <- ggplot(mtcars, aes(cyl, mpg)) +
  geom_point()

Create a simple secondary axis

# secondary axis with labels = y_axis + 10
p +  scale_y_continuous(sec.axis = sec_axis(~.+10))

Create a simple secondary axis with name from primary axis

# same but with axis name same as the one from primary axis
p + scale_y_continuous("Miles/gallon", sec.axis = sec_axis(~.+10, name = derive()))

Create secondary axis by duplicating primary axis

# Duplicate the primary axis
p + scale_y_continuous(sec.axis = dup_axis())

Create secondary axis by passing a formula

# pass in a formula as a shorthand
p + scale_y_continuous(sec.axis = ~.^2)