I have a fix ggplot object (coming from a nice function that I do not want to touch). However, I would like to add some coloring afterwards, thus add new data. How would that be possible?
Here's a simple example.
gg <- ggplot(iris, aes(Sepal.Length, Sepal.Width)) + geom_point()
Now, I want object gg to be colored by Petal.Length,e.g. something like (but that's not working)
gg_colored <- gg + aes(col=Petal.Length)
to obtain:
The solution is to work with the way to handle aesthetics programmatically using aes_string or aes_().
The plot can be equally generated with
data(iris)
gg <- ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width, col=Petal.Length)) +
geom_point()
gg
Or
data(iris)
gg <- ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width))
gg_colored <- gg + geom_point(aes_string(col="Petal.Length"))
gg_colored
With the help of paoloeusebi's anwer, I also found a way to add a new colouring variable (instead of Petal.Length which is inside of iris)
mydat <- gg$data
mydat$col <- rep(LETTERS[1:3], each=50)
gg_colored <- gg + geom_point(data=mydat, aes_string(col="col"))