[R] Ctree Model Variables

[Achim Zeileis]

On Thu, 24 Mar 2011, jdanielnd wrote:

> Hello!
>
> I am not familiar to deal with S4 objects in R, so this question can be
> stupid, but I hope I can get an answer. :P
>
> I'm trying to extract what are the response and explanatory variables from a
> Binary Tree and Random Forest.
>
> I could already extract the response variable from a Binary Tree using the
> response method specified on documentation. But Random Forest didn't had a
> similar method.
>
> And regarding the explanatory variables, I couldn't find any solution at
> all. It seems to be a simple task to extract the explanatory variables from
> a Binary Tree, I just don't know how to deal with the "Slots". In the case
> of the Random Forest, the task can be more complicated since it deal with
> several trees. What I want is the name of all variables used in any tree.
>
> Does someone have any clue on how should I try to solve this?

ctree() contains a "data" slot which contains an object of 
"ModelEnvFormula". This provides the data along with meta-information 
which variables are input and response variables. See

   help("ModelEnvFormula", package = "modeltools")

for details and examples. As a simple application using ctree(), do the 
following: (1) Fit a ctree() named ct. (2) Extract the associated 
ModelEnvFormula call mf. (3) Inspect the components...

R> ct <- ctree(Species ~ ., data = iris)
R> mf <- ct at data
R> mf

A ModelEnvFormula with

   response variable(s):   Species
   input variable(s):      Sepal.Length Sepal.Width Petal.Length Petal.Width
   number of observations: 150

R> head(mf at get("response"))
   Species
1  setosa
2  setosa
3  setosa
4  setosa
5  setosa
6  setosa
R> head(mf at get("input"))
   Sepal.Length Sepal.Width Petal.Length Petal.Width
1          5.1         3.5          1.4         0.2
2          4.9         3.0          1.4         0.2
3          4.7         3.2          1.3         0.2
4          4.6         3.1          1.5         0.2
5          5.0         3.6          1.4         0.2
6          5.4         3.9          1.7         0.4

Best,
Z

> Many thanks!
>
> Joao Daniel Duarte
> UFMG - Brazil
>
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