R: plotting decision tree labels leaves text cut off

Question

(I'm still learning how to handle images in R; this is sort of a continuation of rpart package: Save Decision Tree to PNG )

I'm trying to save a decision tree plot from rpart in PNG form, instead of the provided postscript. My code looks like this:

png("tree.png", width=1000, height=800, antialias="cleartype")
plot(fit, uniform=TRUE, 
   main="Classification Tree")
text(fit, use.n=TRUE, all=TRUE, cex=.8)
dev.off()

but cuts off a little of the labels for the edge nodes on both sides. this isn't a problem in the original post image, which I've converted to png just to check. I've tried using both oma and mar settings in par, which were recommended as solutions for label/text problems, and both added white space around the image but don't show anymore of the labels. Is there any way to get the text to fit?

Answer 1

The rpart.plot package plots rpart trees and automatically takes care of the margin and related issues. Use rpart.plot (instead of plot and text in the rpart package). For example:

library(rpart.plot)
data(ptitanic)
fit <- rpart(survived~., data=ptitanic)
png("tree.png", width=1000, height=800, antialias="cleartype")
rpart.plot(fit, main="Classification Tree")
dev.off()

Answer 2

The default margin is 0. So if your text is a set of words or just a long word, try to put more margin in plot call. For example,

plot(fit, uniform=TRUE,margin=0.2)
text(fit, use.n=TRUE, all=TRUE, cex=.8)

Alternatively, you can adjust text font size by changing cex in text call. For example,

plot(fit, uniform=TRUE)
text(fit,use.n=TRUE, all=TRUE, cex=.7)

Of course, you can adjust both mar in plot call and cex in text call to get what you want.

Answer 3

On rpart man, at rpart() examples the author gives the solution, set par options with xpd = NA:

par(mfrow = c(1,2), xpd = NA)

otherwise on some devices the text is clipped