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