朴素贝叶斯中的因子 (0)？

Question

我正在尝试进行朴素贝叶斯模型预测，无论我尝试什么，结果都是：

<块引用>

头（nb_prey） 因子(0) 级别： str(nb_prey) 0 水平的因子：

这是我的代码：

 intrain <- createDataPartition(y = data.df$left, 
                               p= 0.7, list = FALSE)
    training_set <- data.df[intrain,]
    test_set <-data.df[-intrain,]
    dim(training_set)
    dim(test_set)
    str(test_set)
    test_set$satisfaction_level <- 
    as.factor(test_set$satisfaction_level)

    test_set$last_evaluation <- 
    as.factor(test_set$last_evaluation)

    test_set$number_project <- 
    as.factor(test_set$number_project)

    test_set$average_montly_hours <- 
    as.factor(test_set$average_montly_hours)

    test_set$time_spend_company <- 
    as.factor(test_set$time_spend_company)

    test_set$left <- as.factor(test_set$left)

    # Training the Naive Bayesian Classifier
    nb_model <- naiveBayes(left ~ ., 
                       data = training_set)
    nb_model

    # Predict the new input data based on Naive Bayesian 
    Classifier
    posterior = predict(nb_model, 
                    newdata= test_set, 
                    type = "raw")
    head(posterior)
    str(posterior)
    nb_prey = predict(nb_model, 
                  newdata= test_set, 
                  type ="class")
    head(nb_prey)
    str(nb_prey)