R16

			Classification Trees


# Example - heart disease data

library(rpart)

heart <- read.table("H:/S5600/Data sets/SAheart.txt")
head(heart)

pairs(heart, col=heart$chd+1, pch=heart$chd+1)

heart.cart<-rpart(chd~., data=heart, method="class")
heart.cart

plot(heart.cart)
text(heart.cart, use.n=FALSE, pretty=0)

# Cushings syndrome data

library(MASS)
data(Cushings)
nrow(Cushings)
unk <- (1:27)[Cushings[,3]=="u"]
cush.ltp <- log(Cushings[-unk,1:2])
cush.class <- factor(Cushings[-unk,3])
cush.ltpc <- data.frame(cush.ltp,class=cush.class)

cush.cart <- rpart(class~., data=cush.ltpc, method="class", minsplit=5)

plot(cush.cart)
text(cush.cart, use.n=FALSE, pretty=0)

plot(cush.ltp,col=unclass(cush.class),pch=as.character(cush.class))

segments(1.5757,-4, 1.5757,3)	# Plot first split
segments(1.5757, .6931, 4.5, .6931)	# Second split

# Crabs data

data(crabs)
head(crabs)

crabs.sp <- crabs[,-c(2,3)]
crabs.cart <- rpart(sp ~ ., crabs.sp, method="class")

plot(crabs.cart)
text(crabs.cart, use.n=FALSE, pretty=0)

crabs.cart.pred <- predict(crabs.cart, crabs, type="class")
table(Actual=sp, Classified=crabs.cart.pred)