Add x and y axis to all facet_wrap

Question

It is often desirable to minimize ink in a plot. I have a faceted plot (facet_wrap) and would like to remove as much ink as possible yet maintain readability. I have set it up as I'd like except the x and y axis is not present for the facets (subplots) unless on the far left or bottom. With so much ink removed I believe the eye needs these cues and am asking how to put the x and y axis in all plots within a facet_wrap. Below is my code thus far, the current output and the desired output (red lines are the desired add in):

library(ggplot); library(grid)

ggplot(mtcars, aes(mpg, hp)) + 
    geom_point() + 
    facet_wrap(~carb) +
    theme(panel.grid = element_blank(),
        panel.background = element_rect(fill = "white", colour = "black"), 
        panel.border = element_rect(fill = NA, colour = "white"), 
        axis.line = element_line(),
        strip.background = element_blank(),
        panel.margin = unit(2, "lines"))

Current Plot

Desired Plot

Answer 1

easiest way would be to add segments in each plot panel,

ggplot(mtcars, aes(mpg, hp)) + 
  geom_point() + 
  facet_wrap(~carb) +
  theme_minimal() +
  annotate("segment", x=-Inf, xend=Inf, y=-Inf, yend=-Inf)+
  annotate("segment", x=-Inf, xend=-Inf, y=-Inf, yend=Inf)