How to plot a large ctree() to avoid overlapping nodes

Question

When I plotted the decision tree result from ctree() from party package, the font was too big and the box was also too big. They are overlapping other nodes.

Is there a way to customize the output from plot() so that the box and the font would be smaller ?

Answer 1

The short answer seems to be, no, you cannot change the font size, but there are some good other options.

I know of three possible solutions. First, you can change other parameters in the plot to make it more compact. Second, you can write it to a graphic file and view that file. Third, you can use an alternative implementation of ctree() in the partykit package, which is a newer package by some of the same authors.

Default Plot Example

library(party)
airq <- subset(airquality, !is.na(Ozone))
airct <- ctree(Ozone ~ ., data = airq, 
               controls = ctree_control(maxsurrogate = 3))
plot(airct)  #default plot, some crowding with N hidden on leafs

Simplified plot

# simpler version of plot
plot(airct, type="simple",           # no terminal plots
  inner_panel=node_inner(airct,
       abbreviate = TRUE,            # short variable names
       pval = FALSE,                 # no p-values
       id = FALSE),                  # no id of node
  terminal_panel=node_terminal(airct, 
       abbreviate = TRUE,
       digits = 1,                   # few digits on numbers
       fill = c("white"),            # make box white not grey
       id = FALSE)
   )

This is somewhat better and one might be able to improve it further. To figure out these details, I originally did class(airct) which returned "BinaryTree". Armed with this info, I started reading ?plot.BinaryTree

Write to a file

A second simple solution is to write the plot to a file and then view the file. You may need to play with the settings to find the best fit.

png("airct.png", res=80, height=800, width=1600) 
   plot(airct) 
dev.off()

Plot with partykit package instead

Finally, you can use a newer and not-yet-finished re-implementation of the party package by some of the same authors. At this point (Dec 2012), the only function they have re-done is ctree(). This version allows you to change font size.

    library(partykit) 
    airct <- ctree(Ozone ~ ., data = airq)
    class(airct)  # different class from before
    # "constparty" "party"  
plot(airct, gp = gpar(fontsize = 6),     # font size changed to 6
  inner_panel=node_inner,
  ip_args=list(
       abbreviate = TRUE, 
       id = FALSE)
  )

Here I have left the leafs in their default setting because I have frankly never figured out how to get it to work the way I want. I suspect this has to do with the fact that the package is incomplete (as of Dec 2012). You can read about the plot method starting with ?plot.party