Embedding output from ggplot into another plot [duplicate] - r

Question

This question already has answers here:
Combined plot of ggplot2 (Not in a single Plot), using par() or layout() function? [duplicate]
(3 answers)
R: How should I create Grid-graphics?
(2 answers)
Closed 8 years ago.
I am trying to plot a scatterplot and box plot of two continuous varaibles but am getting an error that says,
Warning message:
In par(fig = c(0, 0.8, 0.55, 1), new = TRUE) :
calling par(new=TRUE) with no plot
The code worked when I simply replaced lines 4-6 of my code with:
plot(mydata$gre, mydata$gpa, xlab="GRE",ylab="GPA")
Here's my code:
mydata <- read.csv("http://www.ats.ucla.edu/stat/data/binary.csv")
par(fig=c(0,0.8,0,0.8), new=TRUE)
#plot(mydata$gre, mydata$gpa, xlab="GRE",ylab="GPA")
d<-ggplot(mydata,aes(x=mydata$gre, y=mydata$gpa))
d<-d+geom_line()
d
par(fig=c(0,0.8,0.55,1), new=TRUE)
boxplot(mydata$gre, horizontal=TRUE, axes=FALSE)
par(fig=c(0.65,1,0,0.8),new=TRUE)
boxplot(mydata$gpa, axes=FALSE)
mtext("Enhanced Scatterplot", side=3, outer=TRUE, line=-3)
Could you please shed some light on what I am doing wrong with regards to ggplot since R isn't recognizing it? What's really weird is that when I type d, the name of my ggplot, I get a plot...

Answer 1

You are attempting to combine grid plots (ggplot2) and base plots (boxplot), but those 2 types of plotting do not play nicely together (hence the cryptic warning).
The simplest solution is to only use one of grid or base plots by replacing the call to ggplot with a call to plot or other functions (base only option) or using grid based functions to do the boxplots (lattice package also uses grid) then use functions from the grid package to arrange the multiple plots.
If you really want to combine grid and base plots then you can use the gridBase package, but this is going to require understanding both types of graphics quite well.