Changing the dataset of a ggplot object

Question

I'm ploting subsets of my data with ggplot2 and I was wondering if I would somehow use all the options already contained in a ggplot object in a subset of the original data. As an example, take this is first plot (code chunk 1):

require(ggplot2)
p <- ggplot(mtcars, aes(mpg, wt, color=factor(cyl))) + geom_point(shape=21, size=4)
print(p)

Now I want to make a second plot with a subset of mtcars, so I would normally do this (code chunk 2):

new_data <- subset(mtcars, disp > 200)
p <- ggplot(new_data, aes(mpg, wt, color=factor(cyl))) + geom_point(shape=19, size=4)
print(p)

It seems a little cumbersome to write all the code again for such a small difference in the dataset. Usually in ggplot you can change some parameters (is that the right term?) making the right operations with the p; for example, i can change the plot colors with p + scale_color_manual(values=rainbow(3)). Of course, this is just a silly example, but it gets really tiresome when I have a really detailed plot, with many tweaks everywhere.

So basically, what I would like to know is if there is some way, like a function x such that I can do this:

p + x(data = new_data)

and get the same as with code chunk 2.

Thanks a lot, Juan

Answer 1

I think it can be done very easily with the ggplot %+% operator.

p <- ggplot(mtcars, aes(mpg, wt, color=factor(cyl))) + geom_point(shape=21, size=4)
print(p)

p2<-p %+% mtcars[mtcars$disp>200,]
print(p2)

Answer 2

If you only want the chunk2:

ggplot(mtcars[mtcars$disp>200,], aes(mpg, wt, color=factor(cyl)))+
geom_point(shape=19, size=4)

If you want both of them in one plot:

ggplot() + 
geom_point(data=mtcars, aes(mpg, wt, color=factor(cyl)),shape=21, size=4)+
geom_point(data=mtcars[mtcars$disp>200,], aes(mpg, wt, color=factor(cyl)),shape=19, size=4)