Summary plot of ggplot2 facets as a facet

Question

It is often the case that we produce facets to decompose the data according to a variable, but that we still would like to see a summary as a stack of the facets. Here is an example:

library(ggplot2)
ggplot(data=iris, aes(x=Sepal.Length,y=Petal.Length)) +
    geom_point(aes(color=Species)) +
    facet_wrap(~Species, ncol=2)

However, I would also like that one of the facets is the overlay of the 3 facets:

ggplot(data=iris, aes(x=Sepal.Length,y=Petal.Length)) +
    geom_point(aes(color=Species)) 

Is there anyway of doing this easily?

Many thanks,

Answer 1

I wrote the following function to duplicate the dataset and create an extra copy under of the data under variable all.

library(ggplot2)

# Create an additional set of data    
CreateAllFacet <- function(df, col){
  df$facet <- df[[col]]
  temp <- df
  temp$facet <- "all"
  return(rbind(temp, df))
}

Instead of overwriting the original facet data column, the function creates a new column called facet. The benefit of this is that we can use the original column to specify the aesthetics of the plot point.

df <- CreateAllFacet(iris, "Species")

ggplot(data=df, aes(x=Sepal.Length,y=Petal.Length)) +
  geom_point(aes(color=Species)) +
  facet_wrap(~facet, ncol=2)

I feel the legend is optional in this case, as it largely duplicates information already available within the plot. It can easily be hidden with the extra line + theme(legend.position = "none")