JAVA高级面试进阶训练营视频教程

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据我们所知，有‘已知的已知’，有些事，我们知道我们知道；我们也知道，有 ‘已知的未知’，也就是说，有些事，我们现在知道我们不知道。但是，同样存在‘不知的不知’——有些事，我们不知道我们不知道。

上一章中分类和回归都属于监督学习。当目标值是未知时，需要使用非监督学习，非监督学习不会学习如何预测目标值。但是，它可以学习数据的结构并找出相似输入的群组，或者学习哪些输入类型可能出现，哪些类型不可能出现。

5.1 异常检测

异常检测常用于检测欺诈、网络攻击、服务器及传感设备故障。在这些应用中，我们要能够找出以前从未见过的新型异常，如新欺诈方式、新入侵方法或新服务器故障模式。

5.2 K均值聚类

聚类是最有名的非监督学习算法，K均值聚类是应用最广泛的聚类算法。它试图在数据集中找出k个簇群。在K均值算法中数据点相互距离一般采用欧氏距离。

在K均值算法中簇群其实是一个点，即组成该簇的所有点的中信。数据点其实就是由所有数值型特征组成的特征向量，简称向量。

簇群的中心称为质心，它是簇群中所有点的算术平均值，因此算法取名K均值。算法开始时选择一些数据点作为簇群的质心。然后把每个数据点分配给最近的质心。接着对每个簇计算该簇所有数据点的平均值，并将其作为该簇的新质心。然后不断重复这个过程。

5.3 网络入侵

统计对各个端口在短时间内被远程访问的次数，就可以得到一个特征，该特征可以很好地预测端口扫描攻击。检测网络入侵是要找到与以往见过的连接不通的连接。K均值可根据每个网络连接的统计属性进行聚类，结果簇定义了历史连接类型，帮我们界定了正常的连接的区域。任何在区域之外的点都是不正常的。

5.4 KDD Cup 1999数据集

KDD Cup是数据挖掘竞赛，由ACM特别兴趣小组举办。1999年主题为网络入侵。
数据下载地址：http://kdd.ics.uci.edu/databases/kddcup99/kddcup99.html
百度云：http://pan.baidu.com/s/1cFqnRS
数据集大小为108，每个连接信息包括发送的字节数、登录次数、TCP错误数等。数据集为CSV格式，每个连接占一行，包括38个特征。
我们关心的问题是找到“未知”的攻击。

5.5 初步尝试聚类

加载数据并查看有哪些类别标号及每类样本有多少：

Scala：

val rawData = sc.textFile("D:/Workspace/AnalysisWithSpark/src/main/java/advanced/chapter5/kddcup.data/kddcup.data.corrected")
rawData.map(_.split(',').last).countByValue().toSeq.sortBy(_._2).reverse.foreach(println)

Java：

 1 //初始化SparkConf
 2 SparkConf sc = new SparkConf().setMaster("local").setAppName("AnomalyDetectionInNetworkTraffic");
 3 System.setProperty("hadoop.home.dir", "D:/Tools/hadoop-2.6.4");
 4 JavaSparkContext jsc = new JavaSparkContext(sc);
 5 
 6 //读入数据
 7 JavaRDD<String> rawData =jsc.textFile("src/main/java/advanced/chapter5/kddcup.data/kddcup.data.corrected");
 8 
 9 //查看有哪些类别标号及每类样本有多少
10 ArrayList<Entry<String, Long>> lineList = new ArrayList<>(rawData.map(line -> line.split(",")[line.split(",").length-1]).countByValue().entrySet());
11 Collections.sort(lineList, (m1, m2) -> m2.getValue().intValue()-m1.getValue().intValue());
12 lineList.forEach(line -> System.out.println(line.getKey() + "," + line.getValue()));

 

结果：
smurf.,2807886
neptune.,1072017
normal.,972781
satan.,15892
ipsweep.,12481
portsweep.,10413
nmap.,2316
back.,2203
warezclient.,1020
teardrop.,979
pod.,264
guess_passwd.,53
buffer_overflow.,30
land.,21
warezmaster.,20
imap.,12
rootkit.,10
loadmodule.,9
ftp_write.,8
multihop.,7
phf.,4
perl.,3
spy.,2

看来用Scala一行能写完的代码用Java还是比较麻烦的。

下面将CSV格式的行拆成列，删除下标从1开始的三个类别型列和最后的标号列。

Scala：

import org.apache.spark.mllib.linalg._
val labelsAndData = rawData.map { line =>
	val buffer = line.split(',').toBuffer
	buffer.remove(1, 3)
	val label = buffer.remove(buffer.length-1)
	val vector = Vectors.dense(buffer.map(_.toDouble).toArray)
	(label,vector)
}
val data = labelsAndData.values.cache()

　　

Java：

 1 //删除下标从1开始的三个类别型列和最后的标号列
 2 JavaRDD<Tuple2<String, Vector>> labelsAndData = rawData.map(line -> {
 3     String[] lineArrya = line.split(",");
 4     double[] vectorDouble = new double[lineArrya.length-4];
 5     for (int i = 0, j=0; i < lineArrya.length; i++) {
 6         if(i==1 || i==2 || i==3 || i==lineArrya.length-1) {
 7             continue;
 8         }
 9         vectorDouble[j] = Double.parseDouble(lineArrya);
10         j++;
11     }
12     String label = lineArrya[lineArrya.length-1];
13     Vector vector = Vectors.dense(vectorDouble);
14     return new Tuple2<String, Vector>(label,vector);
15 });
16 
17 RDD<Vector> data = JavaRDD.toRDD(labelsAndData.map(f -> f._2));

 

对数据进行聚类

Scala：

import org.apache.spark.mllib.clustering._
val kmeans = new KMeans()
val model = kmeans.run(data)
model.clusterCenters.foreach(println)

　　

Java：

1 //聚类
2 KMeans kmeans = new KMeans();
3 KMeansModel model = kmeans.run(data);
4 
5 //聚类结果
6 Arrays.asList(model.clusterCenters()).forEach(v -> System.out.println(v.toJson()));

 

结果：
{"type":1,"values":[48.34019491959669,1834.6215497618625,826.2031900016945,5.7161172049003456E-6,6.487793027561892E-4,7.961734678254053E-6,0.012437658596734055,3.205108575604837E-5,0.14352904910348827,0.00808830584493399,6.818511237273984E-5,3.6746467745787934E-5,0.012934960793560386,0.0011887482315762398,7.430952366370449E-5,0.0010211435092468404,0.0,4.082940860643104E-7,8.351655530445469E-4,334.9735084506668,295.26714620807076,0.17797031701994304,0.17803698940272675,0.05766489875327384,0.05772990937912762,0.7898841322627527,0.021179610609915762,0.02826081009629794,232.98107822302248,189.21428335201279,0.753713389800417,0.030710978823818437,0.6050519309247937,0.006464107887632785,0.1780911843182427,0.17788589813471198,0.05792761150001037,0.05765922142400437]}

{"type":1,"values":[10999.0,0.0,1.309937401E9,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,1.0,1.0,1.0,0.0,0.0,255.0,1.0,0.0,0.65,1.0,0.0,0.0,0.0,1.0,1.0]}

程序输出两个向量，代表K均值将数据聚类成k=2个簇。对本章的数据集，我们知道连接的类型有23个，因此程序肯定没能准确刻画出数据中的不同群组。

查看两个簇中分别包含哪些类型的样本。

Scala：

val clusterLabelCount = labelsAndData.map { case (label,datum) =>
	val cluster = model.predict(datum)
	(cluster,label)
}.countByValue
clusterLabelCount.toSeq.sorted.foreach {
	case ((cluster,label),count) =>
		println(f"$cluster%1s$label%18s$count%8s")
}

　　

Java：

1 ArrayList<Entry<Tuple2<Integer, String>, Long>> clusterLabelCount = new ArrayList<Entry<Tuple2<Integer, String>, Long>>(labelsAndData.map( v -> {
2     int cluster = model.predict(v._2);
3     return new Tuple2<Integer, String>(cluster, v._1);
4 }).countByValue().entrySet());
5 
6 Collections.sort(clusterLabelCount, (m1, m2) -> m2.getKey()._1-m1.getKey()._1);
7 clusterLabelCount.forEach(t -> System.out.println(t.getKey()._1 +"\t"+ t.getKey()._2 +"\t\t"+ t.getValue()));

 

结果：
1 portsweep. 1
0 portsweep. 10412
0 rootkit. 10
0 buffer_overflow. 30
0 phf. 4
0 pod. 264
0 perl. 3
0 spy. 2
0 ftp_write. 8
0 nmap. 2316
0 ipsweep. 12481
0 imap. 12
0 warezmaster. 20
0 satan. 15892
0 teardrop. 979
0 smurf. 2807886
0 neptune. 1072017
0 loadmodule. 9
0 guess_passwd. 53
0 normal. 972781
0 land. 21
0 multihop. 7
0 warezclient. 1020
0 back. 2203

结果显示聚类根本没有任何作用。簇1只有一个数据点！

5.6 K的选择

计算两点距离函数：
Scala：

def distance(a: Vector, b: Vector) =
	math.sqrt(a.toArray.zip(b.toArray).
		map(p => p._1 - p._2).map(d => d * d).sum)

Java：

1 public static double distance(Vector a, Vector b){
2     double[] aArray = a.toArray();
3     double[] bArray = b.toArray();
4     ArrayList<Tuple2<Double, Double>> ab = new ArrayList<Tuple2<Double, Double>>();
5     for (int i = 0; i < a.toArray().length; i++) {
6         ab.add(new Tuple2<Double, Double>(aArray,bArray));
7     }
8     return Math.sqrt(ab.stream().map(x -> x._1-x._2).map(d -> d*d).reduce((r,e) -> r= r+e).get());
9 }

 

计算数据点到簇质心距离函数：
Scala：

def distToCentroid(datum: Vector, model: KMeansModel) = {
	val cluster = model.predict(datum)
	val centroid = model.clusterCenters(cluster)
	distance(centroid, datum)
}

　　

Java：

1 public static double distToCentroid(Vector datum, KMeansModel model) {
2     int cluster = model.predict(datum);
3      Vector[] centroid = model.clusterCenters();
4      return distance(centroid[cluster], datum);
5 }

 

给定k值的模型的平均质心距离函数：
Scala：

import org.apache.spark.rdd._
def clusteringScore(data: RDD[Vector], k: Int) = {
	val kmeans = new KMeans()
	kmeans.setK(k)
	val model = kmeans.run(data)
	data.map(datum => distToCentroid(datum, model)).mean()
}

　　

Java：

1 public static double clusteringScore(JavaRDD<Vector> data, int k) {
2     KMeans kmeans = new KMeans();
3     kmeans.setK(k);
4     KMeansModel model = kmeans.run(JavaRDD.toRDD(data));
5     return data.mapToDouble(datum -> distToCentroid(datum, model)).stats().mean();
6 }

 

对K从5到40进行评估：
Scala：

(5 to 40 by 5).map(k => (k, clusteringScore(data, k))).foreach(println)

　　

Java：
 1 List<Double> list = Arrays.asList(new Integer[]{1, 2, 3, 4, 5, 6, 7, 8}).stream().map(k -> clusteringScore(labelsAndData.map(f -> f._2), k*5)).collect(Collectors.toList()); 2 3 list.forEach(System.out::println); 

要算很久，结果：
1938.8583418059206
1686.4806829850777
1440.0646239087368
1305.763038353858
964.3070891182899
878.7358671386651
571.8923560384558
745.7857049862099

5.11 聚类实战

偷懒了，中间的那些和R相关还有标准化的没有写。

取k=150，聚类结果如下：
149 normal. 4
148 warezclient. 590
148 guess_passwd. 52
148 nmap. 1472
148 portsweep. 378
148 imap. 9
148 ftp_write. 2
…..
97 warezclient. 275
96 normal. 3
95 normal. 1
94 normal. 126
93 normal. 47
92 normal. 52196
92 loadmodule. 1
92 satan. 1
92 buffer_overflow.3
92 guess_passwd. 1
91 normal. 1
90 normal. 3
89 normal. 6
88 normal. 12388
…..
16 normal. 1
15 normal. 11
14 normal. 68
13 normal. 232
12 normal. 1
11 portsweep. 1
10 portsweep. 1
9 warezclient. 59
9 normal. 1
8 normal. 1
7 normal. 1
6 portsweep. 1
5 portsweep. 1
4 portsweep. 1
3 portsweep. 2
2 portsweep. 1
1 portsweep. 1
0 smurf. 527579
0 normal. 345

作为示例，我们在原始数据上进行异常检查：
Scala：

val model = ...
val originalAndData = ...
val anomalies = originalAndData.filter { case (original, datum) =>
	val normalized = normalizeFunction(datum)
	distToCentroid(normalized, model) > threshold
}.keys

　　

Java：

 1         KMeans kmeansF = new KMeans();
 2         kmeansF.setK(150);
 3         KMeansModel modelF = kmeansF.run(data);
 4         
 5         System.out.println("json:---------");
 6         Arrays.asList(modelF.clusterCenters()).forEach(v -> System.out.println(v.toJson()));
 7         
 8         ArrayList<Entry<Tuple2<Integer, String>, Long>> clusterLabelCountF = new ArrayList<Entry<Tuple2<Integer, String>, Long>>(labelsAndData.map( v -> {
 9             int cluster = modelF.predict(v._2);
10             return new Tuple2<Integer, String>(cluster, v._1);
11         }).countByValue().entrySet());
12         
13         Collections.sort(clusterLabelCountF, (m1, m2) -> m2.getKey()._1-m1.getKey()._1);
14         clusterLabelCountF.forEach(t -> System.out.println(t.getKey()._1 +"\t"+ t.getKey()._2 +"\t\t"+ t.getValue()));
15         
16         //距离中心最远的第100个点的距离
17         JavaDoubleRDD distances = labelsAndData.map(f -> f._2).mapToDouble(datum -> distToCentroid(datum, modelF));
18         Double threshold = distances.top(100).get(99);
19         
20         JavaRDD<Tuple2<String, Vector>> result = labelsAndData.filter(t -> distToCentroid(t._2, modelF) > threshold);
21         System.out.println("result:---------");
22         result.foreach(f -> System.out.println(f._2));

 

结果如下：
[2.0,222.0,1703110.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,73.0,255.0,1.0,0.0,0.01,0.03,0.0,0.0,0.0,0.0]
[10.0,194.0,954639.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,255.0,255.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0]
[43.0,528.0,1564759.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,94.0,10.0,0.11,0.76,0.01,0.0,0.0,0.0,0.7,0.1]
[24.0,333.0,1462897.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,2.0,2.0,1.0,0.0,0.5,0.0,0.0,0.0,0.0,0.0]
[60.0,885.0,1581712.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,30.0,8.0,0.27,0.1,0.03,0.0,0.0,0.0,0.0,0.0]
[65.0,693.0,2391949.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,75.0,16.0,0.21,0.05,0.01,0.0,0.0,0.0,0.0,0.0]
[60.0,854.0,1519233.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,113.0,34.0,0.3,0.04,0.01,0.0,0.0,0.0,0.0,0.0]
[107.0,585.0,2661605.0,0.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0,1.0,0.0,0.0,171.0,47.0,0.27,0.02,0.01,0.0,0.0,0.0,0.0,0.0]
……
……

5.12 小结

可以改成StreamingKmeans，它会根据增量对簇进行更新。官方文档中也只有用Scala写的代码，如果需要找Java的话，可以参考我的另外一个项目中的代码： https://github.com/jiangpz/LearnSpark/blob/master/src/main/java/mllib/StreamingKmeansExample.java