# load package
library(XML)
data("ChickWeight")
mydata<- cbind(ID=seq(1, nrow(ChickWeight),by=1),ChickWeight)

start.time <- Sys.time()
xml <- xmlTree()
xml$addTag("document", close=FALSE)

for (i in 1:nrow(mydata)) {
  xml$addNode("chicken", attrs = c(ID = mydata[i,"ID"]), close = FALSE)
  out<- names(mydata)[names(mydata) != "ID"]
      for (j in out) {
    xml$addNode(j, df[i, j])
  }
  xml$closeTag()
}
 xml$closeTag()

# Thats how the XML shoul look like
cat(saveXML(xml))

end.time <- Sys.time()
time.taken <- end.time - start.time
time.taken

#Time difference of 5.847585 secs

# save as matrix
mat<- as.matrix(cbind(ID=seq(1, nrow(ChickWeight),by=1),ChickWeight))

start.time <- Sys.time()
xml <- xmlTree()
xml$addTag("document", close=FALSE)

for (i in 1:dim(mat)[1]) {
  xml$addNode("chicken", attrs = c(ID = mat[i,1]), close = FALSE)
  out<- names(mat)[names(mat) != "ID"]
  for (j in out) {
    xml$addNode(j, mat[i, j])
  }
  xml$closeTag()
}
xml$closeTag()

# Which gives wrong format
cat(saveXML(xml))

end.time <- Sys.time()
time.taken <- end.time - start.time
time.taken

#Time difference of 1.853185 secs