本章为求共同好友
主要的方法是
- 先获得好友的列表，一般为:(100，100 200 300 400)之类
- 进行转换变成[(100,200),(100，100 200 300 400)],[(100,300),(100，100 200 300 400)]之类。
- 之后对key进行排序
- 最后寻找合并之后的key中的value中相同的即可
本章一共有三种实现方式
- 基于传统mapreduce实现
- 基于传统spark实现
- 基于传统的Scala实现
++基于传统mapreduce实现++
//map函数
//获得friend列表
static String getFriends(String[] tokens) {
if (tokens.length == 2) {
return "";
}
StringBuilder builder = new StringBuilder();
for (int i = 1; i < tokens.length; i++) {
builder.append(tokens[i]);
if (i < (tokens.length - 1)) {
builder.append(",");
}
}
return builder.toString();
}
//对key进行排序，确保相同的为一组
static String buildSortedKey(String person, String friend) {
long p = Long.parseLong(person);
long f = Long.parseLong(friend);
if (p < f) {
return person + "," + friend;
} else {
return friend + "," + person;
}
}
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
// parse input, delimiter is a single space
String[] tokens = StringUtils.split(value.toString(), " ");
// create reducer value
String friends = getFriends(tokens);
REDUCER_VALUE.set(friends);
//获得整串friend序列的host
String person = tokens[0];
for (int i = 1; i < tokens.length; i++) {
String friend = tokens[i];
//让person与每个friend逐一的成对，buildSortedKey返回一个string，也是一个text
String reducerKeyAsString = buildSortedKey(person, friend);
REDUCER_KEY.set(reducerKeyAsString);
context.write(REDUCER_KEY, REDUCER_VALUE);
}
}
//reduce函数
@Override
public void reduce(Text key, Iterable values, Context context)
throws IOException, InterruptedException {
Map map = new HashMap();
//对value进行操作
Iterator iterator = values.iterator();
int numOfValues = 0;
while (iterator.hasNext()) {
String friends = iterator.next().toString();
if (friends.equals("")) {
context.write(key, new Text("[]"));
return;
}
addFriends(map, friends);
numOfValues++;
}
// now iterate the map to see how many have numOfValues
List commonFriends = new ArrayList();
for (Map.Entry entry : map.entrySet()) {
//numOfValues为总数，当entry.getValue()与之相用时，则证明两个人的好友列表都有
if (entry.getValue() == numOfValues) {
commonFriends.add(entry.getKey());
}
}
// sen it to output
context.write(key, new Text(commonFriends.toString()));
}
static void addFriends(Map map, String friendsList) {
//获得value中的friends数组
String[] friends = StringUtils.split(friendsList, ",");
for (String friend : friends) {
Integer count = map.get(friend);
if (count == null) {
map.put(friend, 1);
} else {
map.put(friend, ++count);
}
}
}
++基于传统spark实现++
//传统spark实现
public static void main(String[] args) throws Exception {
if (args.length < 1) {
// Spark master URL:
// format: spark://:7077
// example: spark://myserver00:7077
System.err.println("Usage: FindCommonFriends ");
System.exit(1);
}
//String sparkMasterURL = args[0];
//System.out.println("sparkMasterURL="+sparkMasterURL);
String hdfsInputFileName = args[0];
System.out.println("hdfsInputFileName="+hdfsInputFileName);
// create context object
JavaSparkContext ctx = SparkUtil.createJavaSparkContext("FindCommonFriends");
// create the first RDD from input file
JavaRDD records = ctx.textFile(hdfsInputFileName, 1);
// debug0
List debug0 = records.collect();
for (String t : debug0) {
System.out.println("debug0 record="+t);
}
// PairFlatMapFunction
// T => Iterable>
JavaPairRDD,Iterable> pairs =
// T K V
records.flatMapToPair(new PairFlatMapFunction, Iterable>() {
@Override
public Iterator,Iterable>> call(String s) {
//String的输入格式为100，100 200 400 300 etc
String[] tokens = s.split(",");
long person = Long.parseLong(tokens[0]);
String friendsAsString = tokens[1];
String[] friendsTokenized = friendsAsString.split(" ");
//只有一个好友的情况，即两人没有共同的好友
if (friendsTokenized.length == 1) {
Tuple2 key = buildSortedTuple(person, Long.parseLong(friendsTokenized[0]));
return Arrays.asList(new Tuple2,Iterable>(key, new ArrayList())).iterator();
}
//获得出person的好友列表
List friends = new ArrayList();
for (String f : friendsTokenized) {
friends.add(Long.parseLong(f));
}
//发送特定格式的Tuple2
List ,Iterable>> result =
new ArrayList ,Iterable>>();
for (Long f : friends) {
Tuple2 key = buildSortedTuple(person, f);
result.add(new Tuple2, Iterable>(key, friends));
}
return result.iterator();
}
});
// 输出Tuple2
List ,Iterable>> debug1 = pairs.collect();
for (Tuple2,Iterable> t2 : debug1) {
System.out.println("debug1 key="+t2._1+"\t value="+t2._2);
}
//对key进行排序
JavaPairRDD, Iterable>> grouped = pairs.groupByKey();
// debug2
List ,Iterable>>> debug2 = grouped.collect();
for (Tuple2, Iterable>> t2 : debug2) {
System.out.println("debug2 key="+t2._1+"\t value="+t2._2);
}
// Find intersection of all List>
// mapValues[U](f: (V) => U): JavaPairRDD[K, U]
// Pass each value in the key-value pair RDD through a map function without changing the keys;
// this also retains the original RDD's partitioning.
JavaPairRDD, Iterable> commonFriends =
grouped.mapValues(new Function< Iterable>, // input
Iterable // output
>() {
@Override
public Iterable call(Iterable> s) {
Map countCommon = new HashMap();
int size = 0;
for (Iterable iter : s) {
size++;
List list = iterableToList(iter);
if ((list == null) || (list.isEmpty())) {
continue;
}
//
for (Long f : list) {
Integer count = countCommon.get(f);
if (count == null) {
countCommon.put(f, 1);
}
else {
countCommon.put(f, ++count);
}
}
}
// if countCommon.Entry == countCommon.Entry
// then that is a common friend
List finalCommonFriends = new ArrayList();
for (Map.Entry entry : countCommon.entrySet()){
//size表示总数目，当entry的value等于的时候，则表示双方都有的共同好友
if (entry.getValue() == size) {
finalCommonFriends.add(entry.getKey());
}
}
return finalCommonFriends;
}
});
// debug3
List, Iterable>> debug3 = commonFriends.collect();
for (Tuple2, Iterable> t2 : debug3) {
System.out.println("debug3 key="+t2._1+ "\t value="+t2._2);
}
System.exit(0);
}
static Tuple2 buildSortedTuple(long a, long b) {
if (a < b) {
return new Tuple2(a,b);
}
else {
return new Tuple2(b,a);
}
}
static List iterableToList(Iterable iterable) {
List list = new ArrayList();
for (Long item : iterable) {
list.add(item);
}
return list;
}
++基于传统的Scala实现++
//传统Scala实现
def main(args: Array[String]): Unit = {
if (args.size < 2) {
println("Usage: FindCommonFriends ")
sys.exit(1)
}
val sparkConf = new SparkConf().setAppName("FindCommonFriends")
val sc = new SparkContext(sparkConf)
val input = args(0)
val output = args(1)
val records = sc.textFile(input)
val pairs = records.flatMap(s => {
val tokens = s.split(",")
//获得host
val person = tokens(0).toLong
//获得friend列表的list方式
val friends = tokens(1).split("\\s+").map(_.toLong).toList
val result = for {
i <- 0 until friends.size
friend = friends(i)
//这里就以后把host与所有friend的全部生产出来了
} yield {
//这个判断person和friend的方法，也即是在完成key的排序
if (person < friend)
((person, friend), friends)
else
((friend, person), friends)
}
result
})
//对key进行分组
val grouped = pairs.groupByKey()
val commonFriends = grouped.mapValues(iter => {
val friendCount = for {
list <- iter
if !list.isEmpty
friend <- list
//分组类所有人的friend都赋值上1
} yield ((friend, 1))
//分到相用组eg:[a,,1,1] 把这个序列打平编程[a,,（1,1）]
//然后对第二个_.2进行相加，之后大于1的取出它的key
friendCount.groupBy(_._1).mapValues(_.unzip._2.sum).filter(_._2 > 1).map(_._1)
})
// save the result to the file
commonFriends.saveAsTextFile(output)
//Format result for easy viewing
val formatedResult = commonFriends.map(
f => s"(${f._1._1}, ${f._1._2})\t${f._2.mkString("[", ", ", "]")}"
)
formatedResult.foreach(println)
// done!
sc.stop()
}