R-users
E-mail: r-help@r-project.org

   Hi! R-users.

http://finzi.psych.upenn.edu/R/library/mvpart/html/xpred.rpart.html
says:

data(car.test.frame)
fit <- rpart(Mileage ~ Weight, car.test.frame)
xmat <- xpred.rpart(fit)
xerr <- (xmat - car.test.frame$Mileage)^2
apply(xerr, 2, sum)   # cross-validated error estimate
# approx same result as rel. error from printcp(fit)
apply(xerr, 2, sum)/var(car.test.frame$Mileage)
printcp(fit)

I carried out the R object:
function ()
{
#
  library(mvpart)
  xx1 <- c(1,2,3,4,5,6,7,8,9,10)
  xx2 <- c(5,2,1,4,3,6,2,8,2,2)
  xx3 <- c(9,8,3,7,2,3,1,9,1,6)
  yy <- c(1,8,2,7,4,3,1,2,2,8)
  data1 <- data.frame(x1=xx1, x2=xx2, x3=xx3, y=yy)
  set.seed(345)
  rpart.out1 <- rpart(y~., data=data1)
  re1 <- rpart.out1$cptable[,"rel error"]
  print("re1")
  print(re1)

  xmat <- xpred.rpart(rpart.out1)
  xerr <- (xmat - yy)^2
  re2 <- apply(xerr, 2, sum)/var(yy)
  print("re2")
  print(re2)
}

The result is:
"re1"
         1          2          3
1.00000000 0.08891993 0.03258845
"re2"
0.72777002 0.16019126 0.02373425
  11.11111   14.32524   13.12762

Apparently, "re1" is not close to "re2". I would like to know why.

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http://cse.naro.affrc.go.jp/takezawa/intro.html

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