How to extract tree structure from ctree function?

Question

I am trying to extract the tree information from the output of ctree. I tried the Class "BinaryTree" info but with no success. Any input is appreciated.

Thank You

Answer 1

The ctree objects are S4 objects at least at the top, and the tree information is in the "tree" slot. The "tree slot can be access ed with the @ operator. If you take the first example in the help(ctree) page you can get a graphical display with:

plot(airct)

And then you can look are branches of the tree by traversing with list operations. The "leaves" of the tree are descendents of nodes with "terminal"==TRUE:

> airct@tree$right$terminal
[1] FALSE
> airct@tree$left$terminal
[1] FALSE
> airct@tree$right$right$terminal
[1] TRUE
> airct@tree$right$left$terminal
[1] TRUE
> airct@tree$left$left$terminal
[1] TRUE
> airct@tree$left$right$terminal
[1] FALSE

Information at nodes above the leaves can also be recovered:

> airct@tree$left$right
4) Temp <= 77; criterion = 0.997, statistic = 11.599
  5)*  weights = 48 
4) Temp > 77
  6)*  weights = 21 

This is the same information that the nodes function will recover if you know the number of the node:

> nodes(airct,4)
[[1]]
4) Temp <= 77; criterion = 0.997, statistic = 11.599
  5)*  weights = 48 
4) Temp > 77
  6)*  weights = 21 

Answer 2

The mlmeta R package converts fitted ctree models to SAS code. It can be easily adapted to other languages and is generally instructive on the internals of the object.