Duplicating (and modifying) discrete axis in ggplot2

Question

I want to duplicate the left-side Y-axis on a ggplot2 plot onto the right side, and then change the tick labels for a discrete (categorical) axis.

I\'ve read the ans

Answer 1

Take your discrete factor and represent it numerically. Then you can mirror it and relabel the ticks to be the factor levels instead of numbers.

library(ggplot2)

irislabs1 <- levels(iris$Species)
irislabs2 <- c("foo", "bar", "buzz")

ggplot(iris, aes(Sepal.Length, as.numeric(Species))) +
  geom_point() +
  scale_y_continuous(breaks = 1:length(irislabs1),
                     labels = irislabs1,
                     sec.axis = sec_axis(~.,
                                         breaks = 1:length(irislabs2),
                                         labels = irislabs2))

Then fiddle with the expand = argument in the scale as needed to more closely imitate the default discrete scale.