用Java开发的ML库
介绍
在机器学习(Machine Learning,简称ML)领域,Java一直是一种备受争议的开发语言。相比于Python等其他语言,Java的机器学习库相对较少。然而,随着Java的发展和人工智能的兴起,越来越多的机器学习库开始出现,使得Java在ML领域变得更加强大。
本文将介绍一些用Java开发的常用机器学习库,并提供相应的代码示例。
1. Deeplearning4j
Deeplearning4j是一款基于Java的、分布式的深度学习库。它可以用于构建神经网络,并通过大规模数据集进行训练。Deeplearning4j提供了丰富的神经网络模型和优化算法,可以应用于各种机器学习任务。
下面是一个使用Deeplearning4j构建简单的MLP(多层感知机)模型的示例代码:
import org.deeplearning4j.datasets.iterator.impl.MnistDataSetIterator;
import org.deeplearning4j.nn.api.OptimizationAlgorithm;
import org.deeplearning4j.nn.conf.MultiLayerConfiguration;
import org.deeplearning4j.nn.conf.NeuralNetConfiguration;
import org.deeplearning4j.nn.conf.layers.DenseLayer;
import org.deeplearning4j.nn.conf.layers.OutputLayer;
import org.deeplearning4j.nn.multilayer.MultiLayerNetwork;
import org.deeplearning4j.optimize.listeners.ScoreIterationListener;
import org.nd4j.linalg.activations.Activation;
import org.nd4j.linalg.dataset.DataSet;
import org.nd4j.linalg.dataset.api.iterator.DataSetIterator;
import org.nd4j.linalg.lossfunctions.LossFunctions;
public class MLPExample {
public static void main(String[] args) throws Exception {
int numInputs = 784;
int numOutputs = 10;
int batchSize = 64;
int numEpochs = 10;
DataSetIterator mnistTrain = new MnistDataSetIterator(batchSize, true, 12345);
DataSetIterator mnistTest = new MnistDataSetIterator(batchSize, false, 12345);
MultiLayerConfiguration conf = new NeuralNetConfiguration.Builder()
.seed(12345)
.optimizationAlgo(OptimizationAlgorithm.STOCHASTIC_GRADIENT_DESCENT)
.iterations(1)
.learningRate(0.006)
.updater(org.deeplearning4j.nn.conf.Updater.NESTEROVS)
.list()
.layer(0, new DenseLayer.Builder()
.nIn(numInputs)
.nOut(100)
.activation(Activation.RELU)
.build())
.layer(1, new OutputLayer.Builder(LossFunctions.LossFunction.NEGATIVELOGLIKELIHOOD)
.nIn(100)
.nOut(numOutputs)
.activation(Activation.SOFTMAX)
.build())
.pretrain(false)
.backprop(true)
.build();
MultiLayerNetwork net = new MultiLayerNetwork(conf);
net.init();
net.setListeners(new ScoreIterationListener(10));
for (int epoch = 0; epoch < numEpochs; epoch++) {
while (mnistTrain.hasNext()) {
DataSet ds = mnistTrain.next();
net.fit(ds);
}
mnistTrain.reset();
}
Evaluation eval = net.evaluate(mnistTest);
System.out.println(eval.stats());
}
}
2. Java-ML
Java-ML是一个开源的、简单易用的机器学习库,提供了各种常用的机器学习算法和工具。它支持分类、回归、聚类等多种机器学习任务,并提供了特征选择、数据预处理等功能。
下面是一个使用Java-ML进行决策树分类的示例代码:
import java.io.File;
import net.sf.javaml.core.Dataset;
import net.sf.javaml.core.DefaultDataset;
import net.sf.javaml.core.Instance;
import net.sf.javaml.tools.data.FileHandler;
import net.sf.javaml.classification.Classifier;
import net.sf.javaml.classification.tree.RandomForest;
public class DecisionTreeExample {
public static void main(String[] args) throws Exception {
Dataset dataset = FileHandler.loadDataset(new File("data/iris.data"), 4, ",");
Dataset[] datasets = dataset.split(0.8);
Dataset trainingSet = datasets[0];
Dataset testingSet = datasets[1];
Classifier classifier = new RandomForest(100);
classifier.buildClassifier(trainingSet);
int correct = 0;