我试图使用InputMappedClassifier运行一个分类器，因为我知道测试的arff文件缺少训练arff文件中的一些属性。然而，当我运行以下命令时：

java -cp ./weka.jar weka.classifiers.misc.InputMappedClassifier -t aa/lang-train.arff \-T aa/lang-test.arff -W weka.classifiers.trees.J48 -classifications \ weka.classifiers.evaluation.output.prediction.PlainText

它会生成以下异常：

java.lang.IllegalArgumentException: Invalid class index: 2466    at weka.core.Instances.setClassIndex(Instances.java:1293)    at weka.core.converters.ConverterUtils$DataSource.getStructure(ConverterUtils.java:346)    at weka.classifiers.evaluation.output.prediction.AbstractOutput.printClassifications(AbstractOutput.java:625)    at weka.classifiers.evaluation.output.prediction.AbstractOutput.print(AbstractOutput.java:702)    at weka.classifiers.evaluation.Evaluation.evaluateModel(Evaluation.java:1572)    at weka.classifiers.Evaluation.evaluateModel(Evaluation.java:649)    at weka.classifiers.AbstractClassifier.runClassifier(AbstractClassifier.java:297)    at weka.classifiers.misc.InputMappedClassifier.main(InputMappedClassifier.java:943)

如果我去掉-classifications选项，它就能正常运行。我该如何获取分类结果呢？

回答：

你给InputMappedClassifier提供了错误的选项。它抱怨你同时提供了训练数据（-t）和测试数据（-T）。它支持以下选项：

Options specific to weka.classifiers.misc.InputMappedClassifier:-I    Ignore case when matching attribute names and nominal values.-M    Suppress the output of the mapping report.-trim    Trim white space from either end of names before matching.-L <path to model to load>    Path to a model to load. If set, this model    will be used for prediction and any base classifier    specification will be ignored. Environment variables    may be used in the path (e.g. ${HOME}/myModel.model)-W    Full name of base classifier.    (default: weka.classifiers.rules.ZeroR)-output-debug-info    If set, classifier is run in debug mode and    may output additional info to the console-do-not-check-capabilities    If set, classifier capabilities are not checked before classifier is built    (use with caution).

所以你的命令应该像这样：

java -cp ./weka.jar weka.classifiers.misc.InputMappedClassifier -W weka.classifiers.trees.J48 \-t aa/lang-train.arff \-T aa/lang-test.arff \-classifications weka.classifiers.evaluation.output.prediction.PlainText