在 ggplot2 中复制离散轴

Question

The development version of ggplot2 (2.1.0.9001) provides a nice shorthand for creating a secondary axis that is a duplication of the primary axis if the original axis is continuous:

devtools::install_github("hadley/ggplot2")
library(ggplot2)

ggplot(mpg, aes(displ, cyl)) + 
  geom_point() + 
  scale_y_continuous(
    sec.axis = dup_axis()
  )

How can a discrete axis be duplicated?

ggplot(mpg, aes(displ, factor(cyl))) + 
  geom_point() +
  ...?

Answer 1

The switch_axis_position is now deprecated, and in fact is gone. Issues with ggdraw since ggplot2 update

Outdated material: The cowplot library has used to have that that facility:

library(cowplot)
gpv <- ggplot(mpg, aes(displ, factor(cyl))) + 
   geom_point()
ggdraw( switch_axis_position( gpv, axis="y", keep="y"))

Don't forget that you need to print grid-based graphics when sending to a file:

png()
  print(ggdraw(switch_axis_position(gpv, axis="y", keep="y")) )
dev.off()
#quartz 
#     2