java删除Weka ML模型的测试ARFF文件中的最后一个类属性在预测模型中不起作用

Question

基本上，我正在用Java（Weka）构建一个机器学习模型，以检测字符串中的一些模式。我有两个类属性，我试图让我的模型基于这些模式进行预测。当我将属性值保留在ARFF文件中时，我的代码可以工作，但当我取出它并在测试文件中用问号替换它时，代码不能工作。当我这样做时，它会在输出中给我所有相同的值（cfb）。我知道模型不是硬编码的，但出于测试目的，我想删除这些属性值。我已经构建了分类器并评估了模型

 /**
 * Make predictions based on that model. Improve the model
 * 
 * @throws Exception
 */
public void modelPredictions(Instances trainedDataSet, Instances testedDataSet, Classifier classifierType) throws Exception {
    // Get the number of classes
    int numClasses = trainedDataSet.numClasses();
    // print out class values in the training dataset
    for (int i = 0; i < numClasses; i++) {
        // get class string value using the class index
        String classValue = trainedDataSet.classAttribute().value(i);
        System.out.println("Class Value " + i + " is " + classValue);
    }
    // set class index to the last attribute
    // loop through the new dataset and make predictions
    System.out.println("===================");
    System.out.println("Actual Class, NB Predicted");
    for (int i = 0; i < testedDataSet.numInstances(); i++) {
        // get class double value for current instance
        double actualClass = testedDataSet.instance(i).classValue();
        // get class string value using the class index using the class's int value
        String actual = testedDataSet.classAttribute().value((int) actualClass);
        // get Instance object of current instance
        Instance newInst = testedDataSet.instance(i);
        // call classifyInstance, which returns a double value for the class
        double predNB = classifierType.classifyInstance(newInst);
        // use this value to get string value of the predicted class
        String predString = testedDataSet.classAttribute().value((int) predNB);
        System.out.println(actual + ", " + predString);
    }
}

Image of the test ARFF File (Sorry, was getting errors in pasting the file content of the file.

Answer 1

如果将测试集中的实际类替换为问号，这些将被解释为缺少值。Weka中缺少的值用Double.NaN表示。将缺少的值（即Double.NaN）强制转换为int将导致0，这是类的第一个标称值。你的实际类永远是第一类标签

以下代码：

double missing = Utils.missingValue();
System.out.println("missing value as double: " + missing);
System.out.println("missing value as int: " + ((int) missing));

输出如下：

missing value as double: NaN
missing value as int: 0