[R] rpart plot question

[John Field]

Petr Pikal wrote:

Dear all


I am quite confused by rpart plotting. Here is example.


set.seed(1)

y <- (c(rnorm(10), rnorm(10)+2, rnorm(10)+5))

x <- c(rep(c(1,2,5), c(10,10,10))

fit <- rpart(x~y)    ##  NB should be y~x

plot(fit)

text(fit)


Text on first split says x < 3.5 and on the second split x < 1.5 what

I understand:


If x < 3.5 so y is lower and y values go to the left split. OK. But,

sometimes there is


whatever >= nnn and it seems to me that if this condition is true

response variable follow to right split.


try:


y1<-(c(rnorm(10)+5,rnorm(10)+2, rnorm(10)))

fit<-rpart(y1~x)

plot(fit)

text(fit)


Well, I am not sure I express myself clearly. Am I correct that

when there is < sign I shall follow left node but when there is >=

sign I shall follow the right one?


Best regards

Petr Pikal

Petr Pikal

<https://stat.ethz.ch/mailman/listinfo/r-help>petr.pikal at precheza.cz
If instead of rpart you use mvpart, ie

library(mvpart)
fit <- mvpart(y~x, data=data.frame(cbind(x,y)))
plot(fit)
text.rpart(fit,which=4)

then the plot will be much clearer about the condition for splits.

summary(fit) will also help.

Regards,
John

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