Validating the CART model in R

Question

I have built the CART model, however I want to understand how we predict/validate the results with Validation data.

d=sort(sample(nrow(red_data),nrow(red_data)*.7))

#Selecting training sample
train_data=red_data[d,]
test_data=red_data[-d,]
nrow(train_data) #20133#
nrow(test_data)#8629#

rpart(formula = red_status ~ VALUE_CLASS + GAP_1 + cs_rr1_2, 
    data = train_data, method = "class", control = rpart.control(minsplit = 6))

print(cfit)
summary(cfit)

prp(cfit,type=2, extra=106, nn=TRUE,fallen.leaves=TRUE)

This is what I have done.

Could some one help me on this

Answer 1

Since we don't have access to your data, I am guessing that pages 39- 40 of the manual will help you. I'll use the iris data set since it's readily available (and in the documentation):

data(iris)
d <- sort(sample(nrow(iris),nrow(iris)*.7))
(iris.rpart <- rpart(Species ~ . , data = iris, subset = d, method = "class"))
# n= 105 
# 
# node), split, n, loss, yval, (yprob)
# * denotes terminal node
# 
# 1) root 105 68 setosa (0.3523810 0.3333333 0.3142857)  
# 2) Petal.Length< 2.45 37  0 setosa (1.0000000 0.0000000 0.0000000) *
#   3) Petal.Length>=2.45 68 33 versicolor (0.0000000 0.5147059 0.4852941)  
# 6) Petal.Width< 1.75 40  5 versicolor (0.0000000 0.8750000 0.1250000) *
#   7) Petal.Width>=1.75 28  0 virginica (0.0000000 0.0000000 1.0000000) *

# this validation of your test data set (30% of records) shows that the 
# model predicted 44 of 45 correct.  Not bad.
table(predict(iris.rpart, iris[-d,], type = "class"), iris[-d, "Species"])
# setosa versicolor virginica
# setosa         15          0         0
# versicolor      0         15         1
# virginica       0          0        14

?predict.rpart

This could be a comment but. . .

In all seriousness, probably the best help anyone can give you is "read the manual." Also I could point you to the rattle package: this is a pretty simple point and click interface to the rpart package, along with several other modeling tools.

By the way: as noted on the 2nd page of the manual, CART is a trademarked name. "Recursive Partitioning" is a generic name, so you should probably describe your model accordingly.

I hope this helps.