R partykit::ctree offset labels on edges

Question

I am working with ctree and my data set has a covariate of factors that create a node. There are enough factors for that covariate and their names are long enough that they overlap on each other in the edges created at the node. I want to find a way to stop this overlap.

I checked other questions and found one answer that supplies some help. The plot for ctree relies on the grid package and I can use functions to write new labels on the edge. My problem now is that I don't know how to suppress the labels that are printed as default when I plot the tree. I don't know enough about grid or plot.party to figure out which object needs to be suppressed.

An example of my problem in the following image: Code for my example problem:

libary(partykit)
library(tidyverse) #this is here for the mpg data set in next line. not required for partykit
data(mpg)
irt <- ctree(hwy~as.factor(class),data=mpg)
plot(irt)

The resulting 1st node has one edge with "2seater, compact, midsize, subcompact" and the other edge with "minivan, pickup, suv". What I end up seeing in the plot is "2seater, compact, midsize, subcompaminivan, pickup, sub". I've already made the graphics device full screen. (I have other trees that only have one node and so that makes those look odd at the full screen dimension, so I don't want to go back and forth.)

The partial solution I have is

plot(irt, pop=FALSE)
seekViewport("edge1-1")
grid.text("2seater, compact,\n midsize, subcompact")

This stacks "2seater, compact" on top of "midsize, subcompact" and would keep them from overlapping "minivan, pickup, suv". But now, I have the original too-long label still in the plot. And the edge that the label I'm trying fix is attached to has a break in a place that doesn't work with the new stacked label. It would be nice to fix that edge, but the real problem is suppressing the original, too-long label on edge1-1.

Answer 1

The edge labels are drawn by the function edge_simple() which offers various kinds of justifications for the edge labels, see ?edge_simple. The justification is only applied if the edge labels are on average longer than justmin, defaulting to Inf (i.e.: no justification). Various justifications are possible (alternating, increasing, decreasing, or equal).

Thus, in your case the simplest solution is probably to set justmin to a small enough finite value. Alternatively (or additionally) you could also decrease the font size by setting gpar(fontsize = ...). For illustration both examples below have been generated on a 6in x 8in PNG device:

library("partykit")
data("mpg", package = "ggplot2")
irt <- ctree(hwy ~ factor(class), data = mpg)
plot(irt, ep_args = list(justmin = 15))

plot(irt, ep_args = list(justmin = 15), gp = gpar(fontsize = 10))