我刚开始接触机器学习。我尝试使用C5.0模型运行10折交叉验证，并要求代码返回kappa值。

folds = createFolds(mdd.cohort1$edmsemmancomprej, k=10)str(folds)mdd.cohort1_train = mdd.cohort1[-folds$Fold01,]mdd.cohort1_test = mdd.cohort1[folds$Fold01,]library(caret)library(C5.0)library(irr)set.seed(123)folds = createFolds(mdd.cohort1$edmsemmancomprej, k=10)cv_results = lapply(folds, function(x) {mdd.cohort1_train = mdd.cohort1[-x, ] mdd.cohort1_test = mdd.cohort1[x, ] mdd.cohort1_model = C5.0(edmsemmancomprej ~., data = mdd.cohort1_train) mdd.cohort1_pred = predict(mdd.cohort1_model, mdd.cohort1_test) mdd.cohort1_actual = mdd.cohort1_test$edmsemmancomprej kappa = kappa2(data.frame(mdd.cohort1_actual, mdd.cohort1_pred))$value    return(kappa)})

出现了以下错误信息：

Error: unexpected symbol in:"mdd.cohort1_actual = mdd.cohort1_test$edmsemmancomprejkappa = kappa2(data.frame(mdd.cohort1_actual, mdd.cohort1_pred))$value return"

有谁知道发生了什么吗？非常感谢您的帮助！

回答：

没有一个可复现的例子有点困难，但我认为最后那行代码的return语句可能是问题所在。我对您的代码稍作格式调整以提高可读性

library(caret)library(C5.0)library(irr)   folds = createFolds(mdd.cohort1$edmsemmancomprej, k=10)str(folds)mdd.cohort1_train = mdd.cohort1[-folds$Fold01,]mdd.cohort1_test = mdd.cohort1[folds$Fold01,]set.seed(123)folds = createFolds(mdd.cohort1$edmsemmancomprej, k=10)cv_results = lapply(folds, function(x) {  mdd.cohort1_train = mdd.cohort1[-x, ]   mdd.cohort1_test = mdd.cohort1[x, ]   mdd.cohort1_model = C5.0(edmsemmancomprej ~., data = mdd.cohort1_train)   mdd.cohort1_pred = predict(mdd.cohort1_model, mdd.cohort1_test)   mdd.cohort1_actual = mdd.cohort1_test$edmsemmancomprej   kappa = kappa2(data.frame(mdd.cohort1_actual, mdd.cohort1_pred))$value      return(kappa)  })