R help - Aug 2005 - rpart plot question

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)
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
petr.pikal at precheza.cz

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

============================John Field Consulting Pty Ltd
10 High St, Burnside SA 5066, Australia
ph: +61 8 8332 5294 or +61 409 097 586
fax: +61 8 8332 1229
email:  JohnField at ozemail.com.au