Avi - 1 year ago 124
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.

Answer Source

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 ( ) )"
``````
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