modifying ggplot objects after creation

Question

Is there a preferred way to modify ggplot objects after creation?

For example I recommend my students to save the r object together with the pdf file fo

Answer 1

You could use ggplot_build() to alter the plot without the code or data:

Example plot:

data("iris")

p <- ggplot(iris) + 
  aes(x = Sepal.Length, y = Sepal.Width, colour = Species) + 
  geom_point()

Colours are respective to Species.

Disassemble the plot using ggplot_build():

q <- ggplot_build(p)

Take a look at the object q to see what is happening here. To change the colour of the point, you can alter the respective table in q:

q$data[[1]]$colour <- "black"

Reassemble the plot using ggplot_gtable():

q <- ggplot_gtable(q)

And plot it:

plot(q)

Now, the points are black.