Change geom default aesthetics as part of theme component only

Question

For a custom ggplot2 theme I'd like to change the default aesthetic of some geom, say I want red dots instead of black dots.

From this answer I know we can change defaults for a geom using the function update_geom_default but I wonder if it is possible to change the colour only when we call theme_red_dots?

Example of my naive attempt:

library(ggplot2)

theme_red_dots <- function(...) {
  update_geom_defaults("point", list(colour = "red"))
  theme_minimal() +
    theme(...)
}

Looks good here:

ggplot(mtcars, aes(mpg, disp)) + 
  geom_point() + 
  theme_red_dots()

But I'd like the points to be black again when I call

ggplot(mtcars, aes(mpg, disp)) + 
  geom_point()

Thanks in advance!

---

Below is an example of why I thought this could be useful. We can change panel.background to be black fairly easy but this would make it impossible to see the points if we don't map an aesthetic to colour. (The usefulness of this theme_black can certainly be discussed, but I would like to avoid an argument about that.)

theme_black <- function(...) {
  theme_minimal() +
    theme(panel.background = element_rect(fill = "black")) +
    theme(...)
}

# update_geom_defaults("point", list(colour = "black"))
ggplot(mtcars, aes(mpg, disp)) + 
  geom_point() + 
  theme_black()

Changing the colour of the points inside geom_point() is an option here (see @zx8754 answer), but this requires the user of theme_black() to change it, while I am wondering if there is a way to do this right inside theme_*.

Answer 1

Another solution is to detach and reattach ggplot2 (apparently you can do this within custom ggplot2 theme function).

library(ggplot2)

theme_red_dots <- function(...) {
    # wanted theme
    update_geom_defaults("point", list(colour = "red"))

    # Plot
    p <- theme_minimal() + 
        theme(...)

    # Detach and reattach ggplot2
    detach("package:ggplot2", unload = TRUE); library(ggplot2)

    # Return wanted plot
    return(p)
}
# red dots
ggplot(mtcars, aes(mpg, disp)) + 
    geom_point() + 
    theme_red_dots()
# black (default) dots
ggplot(mtcars, aes(mpg, disp)) + 
    geom_point()

Works with wanted theme_black too:

theme_black <- function(...) {
    update_geom_defaults("point", list(colour = "red"))
    p <- theme_minimal() +
        theme(panel.background = element_rect(fill = "black")) +
        theme(...)
    detach("package:ggplot2", unload = TRUE); library(ggplot2)
    return(p)
}

# Plots with black background
ggplot(mtcars, aes(mpg, disp)) + 
    geom_point() + 
    theme_black()

# Plots with default background
ggplot(mtcars, aes(mpg, disp)) + 
    geom_point()

Answer 2

The released version of ggplot2 doesn't currently offer a way to do this. However, this is a fairly old feature request and has been under development since the summer of 2018.