fullOuterJoin

---

官方文件描述：

Perform a full outer join of `this` and `other`. For each element (k, v) in `this`, 
the resulting RDD will either contain all pairs (k, (Some(v), Some(w))) for w in `other`, 
or the pair (k, (Some(v), None)) if no elements in `other` have key k. Similarly, 
for each element (k, w) in `other`, the resulting RDD will either contain all pairs (k, (Some(v), Some(w))) 
for v in `this`, or the pair (k, (None, Some(w))) if no elements in `this` have key k. 
Uses the given Partitioner to partition the output RDD.

函式原型：

def fullOuterJoin[W](other: JavaPairRDD[K, W]): JavaPairRDD[K, (Optional[V], Optional[W])]

def fullOuterJoin[W](other: JavaPairRDD[K, W], numPartitions: Int)
: JavaPairRDD[K, (Optional[V], Optional[W])]

def fullOuterJoin[W](other: JavaPairRDD[K, W], partitioner: Partitioner)
: JavaPairRDD[K, (Optional[V], Optional[W])]

原始碼分析：

def fullOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner)    : RDD[(K, (Option[V], Option[W]))] = self.withScope {  
  this.cogroup(other, partitioner).flatMapValues {    
    case (vs, Seq()) => vs.iterator.map(v => (Some(v), None))    
    case (Seq(), ws) => ws.iterator.map(w => (None, Some(w)))    
    case (vs, ws) => for (v <- vs.iterator; w <- ws.iterator) yield (Some(v), Some(w))  
  }
}

**
從原始碼中可以看出，fullOuterJoin() 與 join() 類似，首先進行 cogroup()， 得到 <K, (Iterable[V1], Iterable[V2])> 型別的 MappedValuesRDD，然後對 Iterable[V1] 和 Iterable[V2] 做笛卡爾集，注意在V1，V2中新增了None，並將集合 flat() 化。
**

例項：

List<Integer> data = Arrays.asList(1, 2, 4, 3, 5, 6, 7);
final Random random = new Random();
JavaRDD<Integer> javaRDD = javaSparkContext.parallelize(data);
JavaPairRDD<Integer,Integer> javaPairRDD = javaRDD.mapToPair(new PairFunction<Integer, Integer, Integer>() {    
  @Override    
  public Tuple2<Integer, Integer> call(Integer integer) throws Exception {        
    return new Tuple2<Integer, Integer>(integer,random.nextInt(10));    
  }
});

//全關聯
JavaPairRDD<Integer,Tuple2<Optional<Integer>,Optional<Integer>>> fullJoinRDD = javaPairRDD.fullOuterJoin(javaPairRDD);
System.out.println(fullJoinRDD);

JavaPairRDD<Integer,Tuple2<Optional<Integer>,Optional<Integer>>> fullJoinRDD1 = javaPairRDD.fullOuterJoin(javaPairRDD,2);
System.out.println(fullJoinRDD1);

JavaPairRDD<Integer,Tuple2<Optional<Integer>,Optional<Integer>>> fullJoinRDD2 = javaPairRDD.fullOuterJoin(javaPairRDD, new Partitioner() {    
  @Override    
  public int numPartitions() {        return 2;    }    
  @Override    
  public int getPartition(Object key) {   return (key.toString()).hashCode()%numPartitions();    }
});
System.out.println(fullJoinRDD2);

leftOuterJoin

---

官方文件描述：

Perform a left outer join of `this` and `other`. For each element (k, v) in `this`, 
the resulting RDD will either contain all pairs (k, (v, Some(w))) for w in `other`, 
or the pair (k, (v, None)) if no elements in `other` have key k. 
Uses the given Partitioner to partition the output RDD.

函式原型：

def leftOuterJoin[W](other: JavaPairRDD[K, W]): JavaPairRDD[K, (V, Optional[W])]

def leftOuterJoin[W](other: JavaPairRDD[K, W], numPartitions: Int)
: JavaPairRDD[K, (V, Optional[W])]

def leftOuterJoin[W](other: JavaPairRDD[K, W], partitioner: Partitioner): JavaPairRDD[K, (V, Optional[W])] 

原始碼分析：

def leftOuterJoin[W](    other: RDD[(K, W)],    partitioner: Partitioner): RDD[(K, (V, Option[W]))] = self.withScope {  
this.cogroup(other, partitioner).flatMapValues { pair =>    
    if (pair._2.isEmpty) {      
      pair._1.iterator.map(v => (v, None))    
    } else {        
      for (v <- pair._1.iterator; w <- pair._2.iterator) yield (v, Some(w))    
    }  
  }
}

**
從原始碼中可以看出，leftOuterJoin() 與 fullOuterJoin() 類似，首先進行 cogroup()， 得到 <K, (Iterable[V1], Iterable[V2])> 型別的 MappedValuesRDD，然後對 Iterable[V1] 和 Iterable[V2] 做笛卡爾集，注意在V1中新增了None，並將集合 flat() 化。
**

例項：

List<Integer> data = Arrays.asList(1, 2, 4, 3, 5, 6, 7);
final Random random = new Random();
JavaRDD<Integer> javaRDD = javaSparkContext.parallelize(data);
JavaPairRDD<Integer,Integer> javaPairRDD = javaRDD.mapToPair(new PairFunction<Integer, Integer, Integer>() {    
  @Override    
  public Tuple2<Integer, Integer> call(Integer integer) throws Exception {        
    return new Tuple2<Integer, Integer>(integer,random.nextInt(10));    
  }
});

//左關聯 JavaPairRDD<Integer,Tuple2<Integer,Optional<Integer>>> leftJoinRDD = javaPairRDD.leftOuterJoin(javaPairRDD);
System.out.println(leftJoinRDD);

JavaPairRDD<Integer,Tuple2<Integer,Optional<Integer>>> leftJoinRDD1 = javaPairRDD.leftOuterJoin(javaPairRDD,2);
System.out.println(leftJoinRDD1);

JavaPairRDD<Integer,Tuple2<Integer,Optional<Integer>>> leftJoinRDD2 = javaPairRDD.leftOuterJoin(javaPairRDD, new Partitioner() {    
    @Override    
    public int numPartitions() {        return 2;    }    
    @Override    
    public int getPartition(Object key) { return (key.toString()).hashCode()%numPartitions();    
  }
});
System.out.println(leftJoinRDD2);

rightOuterJoin

---

官方文件描述：

Perform a right outer join of `this` and `other`. For each element (k, w) in `other`, 
the resulting RDD will either contain all pairs (k, (Some(v), w)) for v in `this`, 
or the pair (k, (None, w)) if no elements in `this` have key k. 
Uses the given Partitioner to partition the output RDD.

函式原型：

def rightOuterJoin[W](other: JavaPairRDD[K, W]): JavaPairRDD[K, (Optional[V], W)]

def rightOuterJoin[W](other: JavaPairRDD[K, W], numPartitions: Int)
: JavaPairRDD[K, (Optional[V], W)]

def rightOuterJoin[W](other: JavaPairRDD[K, W], partitioner: Partitioner): JavaPairRDD[K, (Optional[V], W)]

原始碼分析：

def rightOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner)    : RDD[(K, (Option[V], W))] = self.withScope {  
this.cogroup(other, partitioner).flatMapValues { pair =>    
    if (pair._1.isEmpty) {      
      pair._2.iterator.map(w => (None, w))    
    } else {      
      for (v <- pair._1.iterator; w <- pair._2.iterator) yield (Some(v), w)    
    }  
  }
}

**
從原始碼中可以看出，rightOuterJoin() 與 fullOuterJoin() 類似，首先進行 cogroup()， 得到 <K, (Iterable[V1], Iterable[V2])> 型別的 MappedValuesRDD，然後對 Iterable[V1] 和 Iterable[V2] 做笛卡爾集，注意在V2中新增了None，並將集合 flat() 化。
**

例項：

List<Integer> data = Arrays.asList(1, 2, 4, 3, 5, 6, 7);
final Random random = new Random();
JavaRDD<Integer> javaRDD = javaSparkContext.parallelize(data);
JavaPairRDD<Integer,Integer> javaPairRDD = javaRDD.mapToPair(new PairFunction<Integer, Integer, Integer>() {    
  @Override    
  public Tuple2<Integer, Integer> call(Integer integer) throws Exception {        
    return new Tuple2<Integer, Integer>(integer,random.nextInt(10));    
  }
});

//右關聯
JavaPairRDD<Integer,Tuple2<Optional<Integer>,Integer>> rightJoinRDD = javaPairRDD.rightOuterJoin(javaPairRDD);
System.out.println(rightJoinRDD);

JavaPairRDD<Integer,Tuple2<Optional<Integer>,Integer>> rightJoinRDD1 = javaPairRDD.rightOuterJoin(javaPairRDD,2);
System.out.println(rightJoinRDD1);

JavaPairRDD<Integer,Tuple2<Optional<Integer>,Integer>> rightJoinRDD2 = javaPairRDD.rightOuterJoin(javaPairRDD, new Partitioner() {    
  @Override    
  public int numPartitions() {        return 2;    }    
  @Override    
  public int getPartition(Object key) { return (key.toString()).hashCode()%numPartitions();    }
});
System.out.println(rightJoinRDD2);