R - ggplot geom_dotplot shape option

Question

I want to use geom_dotplot to distinguish two different variables by shape of the dots (rather than colours as the documentation suggests). For example:

library(ggplot2)
set.seed(1)
x = rnorm(20)
y = rnorm(20)
df = data.frame(x,y)
ggplot(data = df) + 
   geom_dotplot(aes(x = x), fill = "red") + 
   geom_dotplot(aes(x=y), fill = "blue")

i.e. to distinguish the x and y in the below example

I want to set all the x to be dots, and y to be triangles.

Is this possible? Thanks!

Answer 1

You could probably hack together something similar to what you want using the information from geom_dotplot plus base R's stripchart function.

#Save the dot plot in an object.

dotplot <- ggplot(data = df) +
geom_dotplot(aes(x = x), fill = "red") +
geom_dotplot(aes(x=y), fill = "blue")

#Use ggplot_build to save information including the x values.
dotplot_ggbuild <- ggplot_build(dotplot)

main_info_from_ggbuild_x <- dotplot_ggbuild$data[[1]]
main_info_from_ggbuild_y <- dotplot_ggbuild$data[[2]]

#Include only the first occurrence of each x value.

main_info_from_ggbuild_x <- 
main_info_from_ggbuild_x[which(duplicated(main_info_from_ggbuild_x$x) == FALSE),]

main_info_from_ggbuild_y <-
main_info_from_ggbuild_y[which(duplicated(main_info_from_ggbuild_y$x) == FALSE),]

#To demonstrate, let's first roughly reproduce the original plot.

stripchart(rep(main_info_from_ggbuild_x$x,
times=main_info_from_ggbuild_x$count),
pch=19,cex=2,method="stack",at=0,col="red")      

stripchart(rep(main_info_from_ggbuild_y$x,
times=main_info_from_ggbuild_y$count),
pch=19,cex=2,method="stack",at=0,col="blue",add=TRUE)

#Now, redo using what we actually want.
#You didn't specify if you want the circles and triangles filled or not. 
#If you want them filled in, just change the pch values.

stripchart(rep(main_info_from_ggbuild_x$x,
times=main_info_from_ggbuild_x$count),
pch=21,cex=2,method="stack",at=0)

stripchart(rep(main_info_from_ggbuild_y$x,
times=main_info_from_ggbuild_y$count),
pch=24,cex=2,method="stack",at=0,add=TRUE)