尝试此C5.0代码时出现此错误

Question

C5.0分类。尝试运行此代码得到此错误。

I've tried nothing since I'm a beginner.

#Sampling the Data
set.seed(1228)
library(C50)
index<-sample(1:dim(dataset)[1],dim(dataset)[1]*.75,replace = FALSE)
training<-dataset[index,]
testing<-dataset[-index,]
cFifty<-C5.0(sentiment~.,data=training,trials=10)
c<-predict(cFifty,testing[,-1])
caret::confusionMatrix(c,testing$sentiment,positive="Yes")
I should get a confusion matrix and stats