[R] Bagging Question

[Majid Javanmard]

Hello

here is the  code implements bagging that I copied from net (
http://www.r-bloggers.com/improve-predictive-performance-in-r-with-bagging/)
:

set.seed(10)
y<-c(1:1000)
x1<-c(1:1000)*runif(1000,min=0,max=2)
x2<-c(1:1000)*runif(1000,min=0,max=2)
x3<-c(1:1000)*runif(1000,min=0,max=2)

lm_fit<-lm(y~x1+x2+x3)
summary(lm_fit)

set.seed(10)
all_data<-data.frame(y,x1,x2,x3)
positions <- sample(nrow(all_data),size=floor((nrow(all_data)/4)*3))
training<- all_data[positions,]
testing<- all_data[-positions,]

lm_fit<-lm(y~x1+x2+x3,data=training)
predictions<-predict(lm_fit,newdata=testing)
error<-sqrt((sum((testing$y-predictions)^2))/nrow(testing))

library(foreach)
length_divisor<-4
iterations<-1000
predictions<-foreach(m=1:iterations,.combine=cbind) %do% {
  training_positions <- sample(nrow(training),
size=floor((nrow(training)/length_divisor)))
  train_pos<-1:nrow(training) %in% training_positions
  lm_fit<-lm(y~x1+x2+x3,data=training[train_pos,])
  predict(lm_fit,newdata=testing)
}
predictions<-rowMeans(predictions)
error<-sqrt((sum((testing$y-predictions)^2))/nrow(testing))


1) How to rank in sequence  Training and Testing in a column ?!
2) How can I have prediction interval for each predicted value ?!

Thanks

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