ggplot add ticks to each plot in a facet_wrap

Question

I'd like to display x-axis ticks on plots in the upper rows in facet_wraps. For example:

library(ggplot2)
ggplot(diamonds, aes(carat)) +  facet_wrap(~ cut, scales = "fixed") +  geom_density()

generates this plot:

I'd like to have ticks as I've drawn in on this plot:

Is there a simple way to achieve this result?

Answer 1

Using scales = "free_x" adds x axes to each plot:

ggplot(diamonds, aes(carat)) + 
    geom_density() + 
    facet_wrap(~cut, scales = "free_x")

However, as you can see and the syntax suggests, it also frees the limits of each plot to adjust automatically, so if you want them all to be consistent, you'll need to set them with xlim, lims or scale_x_continuous:

ggplot(diamonds, aes(carat)) + 
    geom_density() + 
    xlim(range(diamonds$carat)) + 
    # or lims(x = range(diamonds$carat))    
    # or scale_x_continuous(limits = range(diamonds$carat))
    facet_wrap(~cut, scales = "free_x")