weka.core.UnassignedDataset在创建未标记的实例时发生异常

Question

我训练了一个IBK分类器,其中包含我手动创建的一些训练数据,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));

然后我建立了分类器:

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

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

我想创建一个带有未标记类的新实例并对此实例进行分类,我尝试了下面没有运气.

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();
}

我只是得到以下错误

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.如何准确创建未标记的实例？

提前致谢

Answer 1

当您对与数据集无关的新实例进行分类时,您将看到此错误.您必须Instances使用创建的每个新实例与对象关联setDataset.

//Make a place holder Instances
//If you already have access to one, you can skip this step
Instances dataset = new Instances("testdata", attr, 1);
dataset.setClassIndex(classIdx);

DenseInstance newInst = new DenseInstance(1.0,values);

//To associate your instance with Instances object, in this case dataset
newInst.setDataset(dataset); 

在此之后,您可以对新创建的实例进行分类.

double classif = ibk.classifyInstance(newInst);

http://www.cs.tufts.edu/~ablumer/weka/doc/weka.core.Instance.html

详细的实施链接

Answer 2

问题出在这一行:

double classif = ibk.classifyInstance(newInst);

当您尝试进行分类时newInst,Weka会抛出异常,因为newInst没有与之关联的Instances对象(即数据集) - 因此它对其类属性一无所知.

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());