cross validation using pls function in R -

i'm new r , have been trying use following code (thanks stackoverflow) cross validating mars regression. i'm getting error when execute code.

in addition above question, there way print results cross validation?

i appreciate if help.

library(earth) library(pls)  set.seed(1)  k <- 10; result <- 0; folds <- cvsegments(nrow(trees), k);  (fold in 1 : k){   currentfold <- folds[fold][[1]];   fit = earth(volume ~ ., data=trees[-currentfold,])   pred = predict(fit, trees[currentfold,]);   result <- result + table(true=trees[currentfold,3], pred=pred) } 

because k-fold cross validation gets 1 prediction per case (row) in each run, can collect predictions in vector (or matrix, more iterations/repetitions and/or multiple predicted values per case):

library(earth) library(pls) set.seed(1)  k <- 10; folds <- cvsegments(nrow(trees), k); result <- rep (na, nrow (trees))  (fold in 1 : k){   currentfold <- folds[[fold]]   fit = earth(volume ~ ., data=trees[-currentfold,])   result [currentfold] <- predict(fit, trees[currentfold,]); } 

you can @ results @ leisure:

> plot (trees$volume, result)   

> head (cbind (trees, pred.vol = result))   girth height volume  pred.vol 1   8.3     70   10.3  9.701729 2   8.6     65   10.3 10.627089 3   8.8     63   10.2 10.737521 4  10.5     72   16.4 16.313330 5  10.7     81   18.8 21.297516 6  10.8     83   19.7 22.408600