R function to get the rules applied by rpart

Question

iris <- read.csv("iris.csv") #iris data available in R
library(rpart)
iris.rpart <- rpart(Species~Sepal.length+Sepal.width+Petal.width+Petal.length, 
                 data=iris)
plotcp(iris.rpart)
printcp(iris.rpart)
iris.rpart1 <- prune(iris.rpart, cp=0.047)
plot(iris.rpart1,uniform=TRUE)
text(iris.rpart1, use.n=TRUE, cex=0.6)

I have tried to get the rpart done on the iris data. However, is it possible by using some function in R to get the rules applied by rpart for this current tree preparation so that we know how the classifications are made when we add further new points to the data set?

You can read the source code by typing `rpart` alone. It's a long one. — Rich Scriven, Mar 25 '14 at 06:51
@RichardScriven none of the functions from the attributes command? — user3370708, Mar 25 '14 at 07:07
http://stackoverflow.com/questions/22618751/rpart-plot-text-shorter — IRTFM, Mar 25 '14 at 07:14
I think your variable names are incorrect in the `iris.rpart` formula. I tried to edit, but wasn't approved. — Rich Scriven, Mar 25 '14 at 07:29
@RichardScriven I figured it out. I did iris.rpart and got the rules. The last 2 rows of my code helps me generate the graph. I am not being able to get the pdf. could you help me with that? — user3370708, Mar 25 '14 at 09:27

Stephen Milborrow · Answer 1 · 2018-08-10T00:05:30.930

The rpart.plot package has a function rpart.rules for generating a set of rules for a tree. For example

library(rpart.plot)
iris.rpart <- rpart(Species~., data=iris)
rpart.rules(iris.rpart)

gives

   Species  seto vers virg
    setosa [1.00  .00  .00] when Petal.Length <  2.5
versicolor [ .00  .91  .09] when Petal.Length >= 2.5 & Petal.Width <  1.8
 virginica [ .00  .02  .98] when Petal.Length >= 2.5 & Petal.Width >= 1.8

And

options(width=1000)
rpart.predict(iris.rpart, newdata=iris[50:52,], rules=TRUE)

gives you the rule used to make each prediction:

   setosa versicolor virginica
50      1    0.00000  0.000000 because Petal.Length <  2.5
51      0    0.90741  0.092593 because Petal.Length >= 2.5 & Petal.Width <  1.8
52      0    0.90741  0.092593 because Petal.Length >= 2.5 & Petal.Width <  1.8

For more examples see Chapter 4 of the rpart.plot vignette.

R function to get the rules applied by rpart

1 Answers1