R告诉我，我的字符串变量中有新的级别，但是当我打印出级别时，我不会看到它。 ＆＃34;电子＆＃34;是测试和训练数据集中的一个级别。运行日志如下。我还为Predict阶段尝试了不同的数据子集，并将一组不同的级别列为新的。有什么想法吗？
> levels(trainingData$Genre)
[1] "Alternative" "Christian & Gospel" "Country"
[4] "Dance" "Electronic" "Hip Hop / Rap"
[7] "Hip-Hop" "Pop" "Pop in Spanish"
[10] "R&B / Soul" "Rap" "Rock"
[13] "Soul" "Soundtrack"
> levels(testData$Genre)
[1] "Alternative" "Christian & Gospel" "Country"
[4] "Dance" "Electronic" "Hip Hop / Rap"
[7] "Hip-Hop" "Pop" "Pop in Spanish"
[10] "R&B / Soul" "Rap" "Rock"
[13] "Soul" "Soundtrack"
> testData$Genre[id] <- NA
> # Predict
> rankPred <- predict(lmMod, testData)
Error in model.frame.default(Terms, newdata, na.action = na.action, xlev = object$xlevels) :
factor Genre has new levels Electronic
Calls: predict -> predict.lm -> model.frame -> model.frame.default
Execution halted