How do I data get from each facet superimposed on greyed out background data

Question

p <- ggplot(data=mtcars, aes(x=mpg, y=disp))  +geom_point(data=mtcars, color='grey') + geom_point(data=mtcars, aes(color=as.factor(gear)))   +facet_wrap(~gear)

gives this:

But what I want is all data greyed out in the background.

This gets closer but makes background data a new facet, I want it in the background of the 3 facets, not as a new one:

p <- ggplot(data=mtcars, aes(x=mpg, y=disp)) +
  geom_point(data=mtcars %>% mutate(gear = "All"), aes(group=gear), color='grey') +
  geom_point(aes(color=as.factor(gear))) +
  facet_wrap(~gear)

Answer 1

You could use one geom_point with the gear column using select and color them grey. For the second geom_point you could color them by factor like this:

library(ggplot2)
library(dplyr)

p <- ggplot(data=mtcars, aes(x=mpg, y=disp))  + 
  geom_point(data = mtcars %>%
               select(-gear), aes(x = mpg, y = disp), color = 'grey') +
  geom_point(aes(color=as.factor(gear))) +
  facet_wrap(~gear) 
p

^{Created on 2023-03-29 with reprex v2.0.2}

---

If you want to display "all" to the legend with grey color you could assign the name to the aesthetics with color and change the colors with scale_color_manual like this:

library(ggplot2)
library(dplyr)
p <- ggplot(data=mtcars, aes(x=mpg, y=disp))  + 
  geom_point(data = mtcars %>%
               select(-gear), aes(x = mpg, y = disp, color = 'all')) +
  geom_point(aes(color=as.factor(gear))) +
  scale_color_manual(breaks=c("3","4","5","all"),
                    values=c("red", "blue", "green", "grey")) + 
  facet_wrap(~gear) 
p

^{Created on 2023-03-29 with reprex v2.0.2}