mysql - 来自MySql数据库的Weka训练数据

这是我第二次发布关于weka的信息（第一篇发布为here）。我成功使用TextDirectoryLoader为Weka提供了培训和示例测试数据。效果很好。现在，我想将其移至生产环境，以便从mysql表中检索要分类的数据。这就是我的做法：

    TextDirectoryLoader loader = new TextDirectoryLoader();
    loader.setDirectory(new File("c:/Users/Yehia A.Salam/Desktop/dd/training-data"));
    Instances dataRaw = loader.getDataSet();

    StringToWordVector filter = new StringToWordVector();
    filter.setInputFormat(dataRaw);
    Instances dataTraining = Filter.useFilter(dataRaw, filter);

    // Create test data instances[this works, but the sample data now needs to come frm the db instead, see below]
    //loader.setDirectory(new File("c:/Users/Yehia A.Salam/Desktop/dd/test-data"));
    //dataRaw = loader.getDataSet();
    //Instances dataTest = Filter.useFilter(dataRaw, filter);

    InstanceQuery query = new InstanceQuery();
    query.setUsername("myusername");
    query.setPassword("mypassword");
    String sql = "SELECT d.desc FROM deals d WHERE d.j48 = 1";
    query.setQuery(sql);
    Instances dataTest = Filter.useFilter(query.retrieveInstances(), filter);

    // Classify
    J48 model = new J48();
    model.buildClassifier(dataTraining);

    for (int i = 0; i < dataTest.numInstances(); i++) {
             dataTest.instance(i).setClassMissing();
             double cls = model.classifyInstance(dataTest.instance(i));
             dataTest.instance(i).setClassValue(cls);
             System.out.println(cls + " -> " + dataTest.instance(i).classAttribute().value((int) cls));

    }

不幸的是，这行不通，weka在这条线上意外停止：

Instances dataTest = Filter.useFilter(query.retrieveInstances(), filter);

所以我想我的问题是如何改变这部分

// Create test data instances[this works, but the sample data now needs to come frm the db instead, see below]
//loader.setDirectory(new File("c:/Users/Yehia A.Salam/Desktop/dd/test-data"));
//dataRaw = loader.getDataSet();
//Instances dataTest = Filter.useFilter(dataRaw, filter);

到基于sql的数据

InstanceQuery query = new InstanceQuery();
query.setUsername("myusername");
query.setPassword("mypassword");
String sql = "SELECT d.desc FROM deals d WHERE d.j48 = 1";
query.setQuery(sql);
Instances dataTest = Filter.useFilter(query.retrieveInstances(), filter);

请注意，数据库连接没有问题，实际上我得到了正确数量的实例。

感谢帮助，非常亲密。

最佳答案

您的代码使用基于TextDirectoryLoader的Arff Files from Text Collections类。根据他们的帮助文件

"Loads all text files in a directory and
 uses the subdirectory names as class labels.
 The content of the text files will be stored in a String attribute,
 the filename can be stored as well."

请参阅以下code

 double[] newInst = new double[2];
 newInst[0] = (double)data.attribute(0).addStringValue(files[i]);
 ....
 newInst[1] = (double)data.attribute(1).addStringValue(txtStr.toString());
 data.add(new Instance(1.0, newInst));

如您所见，此代码需要2个属性值来添加数据集。但是您的sql仅提供一个属性。

 String sql = "SELECT d.desc FROM deals d WHERE d.j48 = 1";

这可能是代码newInst 1部分中的问题“（java.lang.ArrayIndexOutOfBoundsException）”的原因。 Weka找不到第二个属性。