我尝试通过交叉验证训练随机森林，并使用该caret包来训练 rf：
### variable return_customer = binary variable
idx.train <- createDataPartition(y = known$return_customer, p = 0.8, list = FALSE)
train <- known[idx.train, ]
test <- known[-idx.train, ]
k <- 10
set.seed(123)
model.control <- trainControl(method = "cv", number = k, classProbs = TRUE, summaryFunction = twoClassSummary, allowParallel = TRUE)
rf.parms <- expand.grid(mtry = 1:10)
rf.caret <- train(return_customer~., data = train, method = "rf", ntree = 500, tuneGrid = rf.parms, metric = "ROC", trControl = model.control)
运行该train函数时，我收到此错误代码，但没有缺失值return_customer …