How to set individual x-axis when there is multiple variables in cols with facet_grid_sc

Question

I am trying to customize the scales for each x-axis, but I always get the error below:

Error in .subset2(x, i, exact = exact) : subscript out of bounds

Below is script I am trying to create. Customize the x-axis is needed, because its values are crowded.

library(dplyr)
library(ggplot2)
library(facetscales)

country=factor(c(rep("Japan", 3), rep("US",4), rep("Europe", 7),rep("US",3), "Europe", rep("Japan", 3), rep("US",4), rep("Europe", 3), "US", rep("Europe", 3)))
mtcarros <- mtcars %>% 
  mutate(country=country)

# How should I create the individual scales for the x-axis
scales_x <- list()

ggplot(mtcarros, aes(mpg, cyl))+
  geom_point()+
  facet_grid_sc(gear~carb+country, scales = list(x=scales_x))

So my questions is: How to create the individual scales for the x-axis?

Answer 1

The specific error you report is occurring because you have two variables on the right hand side of your faceting formula - this isn't possible, since it implies a 3-D array of facets rather than a 2-D array (carb would have to be "coming out of the screen"). It is possible to nest facets using other extension packages such as ggh4xto allow a third faceting dimension, but this seems tangential to your main question of how to use facet_grid_sc

To do this, you need to make a named list of scale objects, with one scale for each named level:

scales_x <- list(Japan = scale_x_continuous(label = ~paste(.x, "km/l")),
                 US = scale_x_continuous(label = ~paste(.x, "mpg")),
                 Europe = scale_x_continuous(label = ~paste(.x, "km/l")))

ggplot(mtcarros, aes(mpg, cyl))+
  geom_point()+
  facet_grid_sc(gear~country, scales = list(x=scales_x))

You can set breaks, etc individually for each factor level of each faceting variable.