创建无标签实例时weka.core.UnassignedDatasetException

Question

我使用一些手动创建的训练数据来训练IBK分类器，如下所示：

ArrayList<Attribute> atts = new ArrayList<Attribute>();
ArrayList<String> classVal = new ArrayList<String>();
classVal.add("C1");
classVal.add("C2");
atts.add(new Attribute("a"));
atts.add(new Attribute("b"));
atts.add(new Attribute("c"));
atts.add(new Attribute("d"));
atts.add(new Attribute("@@class@@", classVal));

Instances dataRaw = new Instances("TestInstances", atts, 0);
dataRaw.setClassIndex(dataRaw.numAttributes() - 1);
double[] instanceValue1 = new double[]{3,0,1,0,0};
dataRaw.add(new DenseInstance(1.0, instanceValue1));

double[] instanceValue2 = new double[]{2,1,1,0,0};
dataRaw.add(new DenseInstance(1.0, instanceValue2));

double[] instanceValue3 = new double[]{2,0,2,0,0};
dataRaw.add(new DenseInstance(1.0, instanceValue3));

double[] instanceValue4 = new double[]{1,3,0,0,1};
dataRaw.add(new DenseInstance(1.0, instanceValue4));

double[] instanceValue5 = new double[]{0,3,1,0,1};
dataRaw.add(new DenseInstance(1.0, instanceValue5));

double[] instanceValue6 = new double[]{0,2,1,1,1};
dataRaw.add(new DenseInstance(1.0, instanceValue6));

然后我建立分类器：

IBk ibk = new IBk();
try {
    ibk.buildClassifier(dataRaw);

} catch (Exception e) {
    e.printStackTrace();
}

我想用未标记的类创建一个新实例并对该实例进行分类，但我没有运气尝试了以下方法。

IBk ibk = new IBk();
try {
    ibk.buildClassifier(dataRaw);
    double[] values = new double[]{3,1,0,0,-1};
    DenseInstance newInst = new DenseInstance(1.0,values);
    double classif = ibk.classifyInstance(newInst);
    System.out.println(classif);
} catch (Exception e) {
    e.printStackTrace();
}

我刚收到以下错误

weka.core.UnassignedDatasetException: DenseInstance doesn't have access to a dataset!
at weka.core.AbstractInstance.classAttribute(AbstractInstance.java:98)
at weka.classifiers.AbstractClassifier.classifyInstance(AbstractClassifier.java:74)
at TextCategorizationTest.instancesWithDoubleValues(TextCategorizationTest.java:136)
at TextCategorizationTest.main(TextCategorizationTest.java:33)

看起来我在创建新实例时做错了什么。如何准确创建一个未标记的实例？

提前致谢

Answer 1

问题在于此行：

double classif = ibk.classifyInstance(newInst);

当您尝试分类时newInst，Weka会引发异常，因为newInst没有与之关联的Instances对象（即，数据集）-因此，它对类属性一无所知。

您应该首先创建一个类似于dataRaw的新Instances对象，向其添加未标记的实例，设置类索引，然后才尝试对其进行分类，例如：

Instances dataUnlabeled = new Instances("TestInstances", atts, 0);
dataUnlabeled.add(newInst);
dataUnlabeled.setClassIndex(dataUnlabeled.numAttributes() - 1);        
double classif = ibk.classifyInstance(dataUnlabeled.firstInstance());