在Java中使用weka：产生折叠交叉验证

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翻译最新推荐文章于 2026-07-20 18:45:00 发布 4.2k 阅读 AI 写同款· GEO 优化 ›

Java集成Weka做线性回归的例子线性回归在数据挖掘领域应也是非常常见，即根据现有的数据集（行向量组成的矩阵），（训练）模拟出一个合适的规律（函数），来推测任何新给出的数据组合（向量）应该得到的值。具体的描述可以参见各种博客，怎么推导的看来看去一知半解，但总而言之结果也简单，就是计算得到一个“适当”的多元线性函数Y=a0+a1*x1+a2*x2+a3*x3+…+ak*xk。阅读详情

水平有限，随便翻译，能看就行

原址：http://weka.wikispaces.com/Generating+cross-validation+folds+%28Java+approach%29

文章主要讲述了如何直接使用wekaAPI产生交叉验证训练/测试splits

使用如下变量：

Instances data =  ...;   // contains the full dataset we wann create train/test sets from
 int seed = ...;          // the seed for randomizing the data
 int folds = ...;         // the number of folds to generate, >=2

随机化数据

首先随机化你的数据

Random rand = new Random(seed);   // create seeded number generator
 randData = new Instances(data);   // create copy of original data
 randData.randomize(rand);         // randomize data with number generator

如果你的数据含有 nominal类，并且你想要使用分层交叉验证

randData.stratify(folds);

产生折叠

单步运行

接下来我们要做的事情就是创建训练和测试集

for (int n = 0; n < folds; n++) {
   Instances train = randData.trainCV(folds, n);
   Instances test = randData.testCV(folds, n);
 
   // further processing, classification, etc.
   ...
 }

备注：上面的代码由 weka.filters.supervised.instance.StratifiedRemoveFolds过滤器使用，weka.classifiers.Evaluation类和Explorer/Experimenter将会使用这个方法来得到训练集。

 Instances train = randData.trainCV(folds, n, rand);

多步运行

上面的例子演示了单步运行交叉验证，如果你想运行10次10折交叉验证使用下面的循环：

Instances data = ...;  // our dataset again, obtained from somewhere
 int runs = 10;
 for (int i = 0; i < runs; i++) {
   seed = i+1;  // every run gets a new, but defined seed value
 
   // see: randomize the data
   ...
 
   // see: generate the folds
   ...
 }

下面给出几个具体的例子

CrossValidationSingleRun.java

import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource;
import weka.core.Utils;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;

import java.util.Random;

/**
 * Performs a single run of cross-validation.
 *
 * Command-line parameters:
 * <ul>
 *    <li>-t filename - the dataset to use</li>
 *    <li>-x int - the number of folds to use</li>
 *    <li>-s int - the seed for the random number generator</li>
 *    <li>-c int - the class index, "first" and "last" are accepted as well;
 *    "last" is used by default</li>
 *    <li>-W classifier - classname and options, enclosed by double quotes; 
 *    the classifier to cross-validate</li>
 * </ul>
 *
 * Example command-line:
 * <pre>
 * java CrossValidationSingleRun -t anneal.arff -c last -x 10 -s 1 -W "weka.classifiers.trees.J48 -C 0.25"
 * </pre>
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 */
public class CrossValidationSingleRun {

  /**
   * Performs the cross-validation. See Javadoc of class for information
   * on command-line parameters.
   *
   * @param args        the command-line parameters
   * @throws Excecption if something goes wrong
   */
  public static void main(String[] args) throws Exception {
    // loads data and set class index
    Instances data = DataSource.read(Utils.getOption("t", args));
    String clsIndex = Utils.getOption("c", args);
    if (clsIndex.length() == 0)
      clsIndex = "last";
    if (clsIndex.equals("first"))
      data.setClassIndex(0);
    else if (clsIndex.equals("last"))
      data.setClassIndex(data.numAttributes() - 1);
    else
      data.setClassIndex(Integer.parseInt(clsIndex) - 1);

    // classifier
    String[] tmpOptions;
    String classname;
    tmpOptions     = Utils.splitOptions(Utils.getOption("W", args));
    classname      = tmpOptions[0];
    tmpOptions[0]  = "";
    Classifier cls = (Classifier) Utils.forName(Classifier.class, classname, tmpOptions);

    // other options
    int seed  = Integer.parseInt(Utils.getOption("s", args));
    int folds = Integer.parseInt(Utils.getOption("x", args));

    // randomize data
    Random rand = new Random(seed);
    Instances randData = new Instances(data);
    randData.randomize(rand);
    if (randData.classAttribute().isNominal())
      randData.stratify(folds);

    // perform cross-validation
    Evaluation eval = new Evaluation(randData);
    for (int n = 0; n < folds; n++) {
      Instances train = randData.trainCV(folds, n);
      Instances test = randData.testCV(folds, n);
      // the above code is used by the StratifiedRemoveFolds filter, the
      // code below by the Explorer/Experimenter:
      // Instances train = randData.trainCV(folds, n, rand);

      // build and evaluate classifier
      Classifier clsCopy = Classifier.makeCopy(cls);
      clsCopy.buildClassifier(train);
      eval.evaluateModel(clsCopy, test);
    }

    // output evaluation
    System.out.println();
    System.out.println("=== Setup ===");
    System.out.println("Classifier: " + cls.getClass().getName() + " " + Utils.joinOptions(cls.getOptions()));
    System.out.println("Dataset: " + data.relationName());
    System.out.println("Folds: " + folds);
    System.out.println("Seed: " + seed);
    System.out.println();
    System.out.println(eval.toSummaryString("=== " + folds + "-fold Cross-validation ===", false));
  }
}

CrossValidationSingleRunVariant.java

import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource;
import weka.core.Utils;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;

import java.util.Random;

/**
 * Performs a single run of cross-validation. Outputs the Confusion matrices
 * for each single fold.
 *
 * Command-line parameters:
 * <ul>
 *    <li>-t filename - the dataset to use</li>
 *    <li>-x int - the number of folds to use</li>
 *    <li>-s int - the seed for the random number generator</li>
 *    <li>-c int - the class index, "first" and "last" are accepted as well;
 *    "last" is used by default</li>
 *    <li>-W classifier - classname and options, enclosed by double quotes; 
 *    the classifier to cross-validate</li>
 * </ul>
 *
 * Example command-line:
 * <pre>
 * java CrossValidationSingleRun -t anneal.arff -c last -x 10 -s 1 -W "weka.classifiers.trees.J48 -C 0.25"
 * </pre>
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 */
public class CrossValidationSingleRunVariant {

  /**
   * Performs the cross-validation. See Javadoc of class for information
   * on command-line parameters.
   *
   * @param args        the command-line parameters
   * @throws Excecption if something goes wrong
   */
  public static void main(String[] args) throws Exception {
    // loads data and set class index
    Instances data = DataSource.read(Utils.getOption("t", args));
    String clsIndex = Utils.getOption("c", args);
    if (clsIndex.length() == 0)
      clsIndex = "last";
    if (clsIndex.equals("first"))
      data.setClassIndex(0);
    else if (clsIndex.equals("last"))
      data.setClassIndex(data.numAttributes() - 1);
    else
      data.setClassIndex(Integer.parseInt(clsIndex) - 1);

    // classifier
    String[] tmpOptions;
    String classname;
    tmpOptions     = Utils.splitOptions(Utils.getOption("W", args));
    classname      = tmpOptions[0];
    tmpOptions[0]  = "";
    Classifier cls = (Classifier) Utils.forName(Classifier.class, classname, tmpOptions);

    // other options
    int seed  = Integer.parseInt(Utils.getOption("s", args));
    int folds = Integer.parseInt(Utils.getOption("x", args));

    // randomize data
    Random rand = new Random(seed);
    Instances randData = new Instances(data);
    randData.randomize(rand);
    if (randData.classAttribute().isNominal())
      randData.stratify(folds);

    // perform cross-validation
    System.out.println();
    System.out.println("=== Setup ===");
    System.out.println("Classifier: " + cls.getClass().getName() + " " + Utils.joinOptions(cls.getOptions()));
    System.out.println("Dataset: " + data.relationName());
    System.out.println("Folds: " + folds);
    System.out.println("Seed: " + seed);
    System.out.println();
    Evaluation evalAll = new Evaluation(randData);
    for (int n = 0; n < folds; n++) {
      Evaluation eval = new Evaluation(randData);
      Instances train = randData.trainCV(folds, n);
      Instances test = randData.testCV(folds, n);
      // the above code is used by the StratifiedRemoveFolds filter, the
      // code below by the Explorer/Experimenter:
      // Instances train = randData.trainCV(folds, n, rand);

      // build and evaluate classifier
      Classifier clsCopy = Classifier.makeCopy(cls);
      clsCopy.buildClassifier(train);
      eval.evaluateModel(clsCopy, test);
      evalAll.evaluateModel(clsCopy, test);

      // output evaluation
      System.out.println();
      System.out.println(eval.toMatrixString("=== Confusion matrix for fold " + (n+1) + "/" + folds + " ===\n"));
    }

    // output evaluation
    System.out.println();
    System.out.println(evalAll.toSummaryString("=== " + folds + "-fold Cross-validation ===", false));
  }
}

CrossValidationMultipleRuns.java

import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource;
import weka.core.Utils;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;

import java.util.Random;

/**
 * Performs multiple runs of cross-validation.
 *
 * Command-line parameters:
 * <ul>
 *    <li>-t filename - the dataset to use</li>
 *    <li>-x int - the number of folds to use</li>
 *    <li>-r int - the number of runs to perform</li>
 *    <li>-c int - the class index, "first" and "last" are accepted as well;
 *    "last" is used by default</li>
 *    <li>-W classifier - classname and options, enclosed by double quotes; 
 *    the classifier to cross-validate</li>
 * </ul>
 *
 * Example command-line:
 * <pre>
 * java CrossValidationMultipleRuns -t labor.arff -c last -x 10 -r 10 -W "weka.classifiers.trees.J48 -C 0.25"
 * </pre>
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 */
public class CrossValidationMultipleRuns {

  /**
   * Performs the cross-validation. See Javadoc of class for information
   * on command-line parameters.
   *
   * @param args        the command-line parameters
   * @throws Excecption if something goes wrong
   */
  public static void main(String[] args) throws Exception {
    // loads data and set class index
    Instances data = DataSource.read(Utils.getOption("t", args));
    String clsIndex = Utils.getOption("c", args);
    if (clsIndex.length() == 0)
      clsIndex = "last";
    if (clsIndex.equals("first"))
      data.setClassIndex(0);
    else if (clsIndex.equals("last"))
      data.setClassIndex(data.numAttributes() - 1);
    else
      data.setClassIndex(Integer.parseInt(clsIndex) - 1);

    // classifier
    String[] tmpOptions;
    String classname;
    tmpOptions     = Utils.splitOptions(Utils.getOption("W", args));
    classname      = tmpOptions[0];
    tmpOptions[0]  = "";
    Classifier cls = (Classifier) Utils.forName(Classifier.class, classname, tmpOptions);

    // other options
    int runs  = Integer.parseInt(Utils.getOption("r", args));
    int folds = Integer.parseInt(Utils.getOption("x", args));

    // perform cross-validation
    for (int i = 0; i < runs; i++) {
      // randomize data
      int seed = i + 1;
      Random rand = new Random(seed);
      Instances randData = new Instances(data);
      randData.randomize(rand);
      if (randData.classAttribute().isNominal())
        randData.stratify(folds);

      Evaluation eval = new Evaluation(randData);
      for (int n = 0; n < folds; n++) {
        Instances train = randData.trainCV(folds, n);
        Instances test = randData.testCV(folds, n);
        // the above code is used by the StratifiedRemoveFolds filter, the
        // code below by the Explorer/Experimenter:
        // Instances train = randData.trainCV(folds, n, rand);

        // build and evaluate classifier
        Classifier clsCopy = Classifier.makeCopy(cls);
        clsCopy.buildClassifier(train);
        eval.evaluateModel(clsCopy, test);
      }

      // output evaluation
      System.out.println();
      System.out.println("=== Setup run " + (i+1) + " ===");
      System.out.println("Classifier: " + cls.getClass().getName() + " " + Utils.joinOptions(cls.getOptions()));
      System.out.println("Dataset: " + data.relationName());
      System.out.println("Folds: " + folds);
      System.out.println("Seed: " + seed);
      System.out.println();
      System.out.println(eval.toSummaryString("=== " + folds + "-fold Cross-validation run " + (i+1) + "===", false));
    }
  }
}

CrossValidationAddPrediction.java

import weka.core.Instances;
import weka.core.converters.ConverterUtils.DataSource;
import weka.core.converters.ConverterUtils.DataSink;
import weka.core.Utils;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;
import weka.filters.Filter;
import weka.filters.supervised.attribute.AddClassification;

import java.util.Random;

/**
 * Performs a single run of cross-validation and adds the prediction on the 
 * test set to the dataset.
 *
 * Command-line parameters:
 * <ul>
 *    <li>-t filename - the dataset to use</li>
 *    <li>-o filename - the output file to store dataset with the predictions
 *    in</li>
 *    <li>-x int - the number of folds to use</li>
 *    <li>-s int - the seed for the random number generator</li>
 *    <li>-c int - the class index, "first" and "last" are accepted as well;
 *    "last" is used by default</li>
 *    <li>-W classifier - classname and options, enclosed by double quotes; 
 *    the classifier to cross-validate</li>
 * </ul>
 *
 * Example command-line:
 * <pre>
 * java CrossValidationAddPrediction -t anneal.arff -c last -o predictions.arff -x 10 -s 1 -W "weka.classifiers.trees.J48 -C 0.25"
 * </pre>
 *
 * @author FracPete (fracpete at waikato dot ac dot nz)
 */
public class CrossValidationAddPrediction {

  /**
   * Performs the cross-validation. See Javadoc of class for information
   * on command-line parameters.
   *
   * @param args        the command-line parameters
   * @throws Excecption if something goes wrong
   */
  public static void main(String[] args) throws Exception {
    // loads data and set class index
    Instances data = DataSource.read(Utils.getOption("t", args));
    String clsIndex = Utils.getOption("c", args);
    if (clsIndex.length() == 0)
      clsIndex = "last";
    if (clsIndex.equals("first"))
      data.setClassIndex(0);
    else if (clsIndex.equals("last"))
      data.setClassIndex(data.numAttributes() - 1);
    else
      data.setClassIndex(Integer.parseInt(clsIndex) - 1);

    // classifier
    String[] tmpOptions;
    String classname;
    tmpOptions     = Utils.splitOptions(Utils.getOption("W", args));
    classname      = tmpOptions[0];
    tmpOptions[0]  = "";
    Classifier cls = (Classifier) Utils.forName(Classifier.class, classname, tmpOptions);

    // other options
    int seed  = Integer.parseInt(Utils.getOption("s", args));
    int folds = Integer.parseInt(Utils.getOption("x", args));

    // randomize data
    Random rand = new Random(seed);
    Instances randData = new Instances(data);
    randData.randomize(rand);
    if (randData.classAttribute().isNominal())
      randData.stratify(folds);

    // perform cross-validation and add predictions
    Instances predictedData = null;
    Evaluation eval = new Evaluation(randData);
    for (int n = 0; n < folds; n++) {
      Instances train = randData.trainCV(folds, n);
      Instances test = randData.testCV(folds, n);
      // the above code is used by the StratifiedRemoveFolds filter, the
      // code below by the Explorer/Experimenter:
      // Instances train = randData.trainCV(folds, n, rand);

      // build and evaluate classifier
      Classifier clsCopy = Classifier.makeCopy(cls);
      clsCopy.buildClassifier(train);
      eval.evaluateModel(clsCopy, test);

      // add predictions
      AddClassification filter = new AddClassification();
      filter.setClassifier(cls);
      filter.setOutputClassification(true);
      filter.setOutputDistribution(true);
      filter.setOutputErrorFlag(true);
      filter.setInputFormat(train);
      Filter.useFilter(train, filter);  // trains the classifier
      Instances pred = Filter.useFilter(test, filter);  // perform predictions on test set
      if (predictedData == null)
        predictedData = new Instances(pred, 0);
      for (int j = 0; j < pred.numInstances(); j++)
        predictedData.add(pred.instance(j));
    }

    // output evaluation
    System.out.println();
    System.out.println("=== Setup ===");
    System.out.println("Classifier: " + cls.getClass().getName() + " " + Utils.joinOptions(cls.getOptions()));
    System.out.println("Dataset: " + data.relationName());
    System.out.println("Folds: " + folds);
    System.out.println("Seed: " + seed);
    System.out.println();
    System.out.println(eval.toSummaryString("=== " + folds + "-fold Cross-validation ===", false));

    // output "enriched" dataset
    DataSink.write(Utils.getOption("o", args), predictedData);
  }
}

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