Avi Avi - 3 months ago 22
R Question

How to get properties of rpart (CART) decision tree in R?

I have the following rpart:

library("partykit")
library("rpart")
res = rpart(Species ~., data = iris)
pres <- as.party(res)

> pres

Model formula:
Species ~ Sepal.Length + Sepal.Width + Petal.Length + Petal.Width

Fitted party:
[1] root
| [2] Petal.Length < 2.45: setosa (n = 50, err = 0.0%)
| [3] Petal.Length >= 2.45
| | [4] Petal.Width < 1.75: versicolor (n = 54, err = 9.3%)
| | [5] Petal.Width >= 1.75: virginica (n = 46, err = 2.2%)

Number of inner nodes: 2
Number of terminal nodes: 3


I would like to take each split node and its value and write them in the following order:

{Petal.Length 2.45 {Petal.Width 1.75} }


Where each level is separated from its higher level by {.
I would like to do it very similar to what was done for J48 here.

Avi Avi
Answer

The solution is:

library("partykit")
pres <- as.party(res)


partykit:::.list.rules.party(pres)

nam <- names(pres$data)
tr <- as.list(pres$node)
str <- "("
update_str <- function(x) {
  if(is.null(x$kids)) {
    str <<- paste(str, ")")
  } else {
    str <<- paste(str, nam[x$split$varid], x$split$breaks, "(")
    for(i in x$kids) update_str(tr[[i]])
  }
}
update_str(tr[[1]])
> str
[1] "( Petal.Length 2.45 ( ) Petal.Width 1.75 ( ) )"