trainControl(
method = "boot",
number = ifelse(method == "cv", 10, 25),
verboseIter = TRUE,
returnData = TRUE,
p = 0.5,
index = NULL)boot, cv,
LOOCV, LGOCV (for repeated training/test splits), or
oob (only for random forest, bagged trees, bagged earth, bagged flexible discriminant analysis,