转账自：https://blog.csdn.net/t1dmzks/article/details/70557249

subtractByKey

函数定义

def subtractByKey[W](other: RDD[(K, W)])(implicit arg0: ClassTag[W]): RDD[(K, V)]

def subtractByKey[W](other: RDD[(K, W)], numPartitions: Int)(implicit arg0: ClassTag[W]): RDD[(K, V)]

def subtractByKey[W](other: RDD[(K, W)], p: Partitioner)(implicit arg0: ClassTag[W]): RDD[(K, V)]

类似于subtrac，删掉 RDD 中键与 other RDD 中的键相同的元素

join

函数定义

def join[W](other: RDD[(K, W)]): RDD[(K, (V, W))]

def join[W](other: RDD[(K, W)], numPartitions: Int): RDD[(K, (V, W))]

def join[W](other: RDD[(K, W)], partitioner: Partitioner): RDD[(K, (V, W))]

• RDD1.join(RDD2) 

可以把RDD1,RDD2中的相同的key给连接起来，类似于sql中的join操作

leftOuterJoin

def leftOuterJoin[W](other: RDD[(K, W)]): RDD[(K, (V, Option[W]))]

def leftOuterJoin[W](other: RDD[(K, W)], numPartitions: Int): RDD[(K, (V, Option[W]))]

def leftOuterJoin[W](other: RDD[(K, W)], partitioner: Partitioner): RDD[(K, (V, Option[W]))]

直接看图即可 
对两个 RDD 进行连接操作，类似于sql中的左外连接

rightOuterJoin

对两个 RDD 进行连接操作，类似于sql中的右外连接，存在的话，value用的Some, 不存在用的None,具体的看上面的图和下面的代码即可

代码示例

scala语言

    scala> val rdd = sc.makeRDD(Array((1,2),(3,4),(3,6)))
    scala> val other = sc.makeRDD(Array((3,9)))

    scala>  rdd.subtractByKey(other).collect()
    res0: Array[(Int, Int)] = Array((1,2))

    scala> rdd.join(other).collect()
    res1: Array[(Int, (Int, Int))] = Array((3,(4,9)), (3,(6,9)))

    scala> rdd.leftOuterJoin(other).collect()
    res2: Array[(Int, (Int, Option[Int]))] = Array((1,(2,None)), (3,(4,Some(9))), (3,(6,Some(9))))

    scala> rdd.rightOuterJoin(other).collect()
    res3: Array[(Int, (Option[Int], Int))] = Array((3,(Some(4),9)), (3,(Some(6),9)))

java语言

    JavaRDD<Tuple2<Integer,Integer>> rddPre = sc.parallelize(Arrays.asList(new Tuple2(1,2)
            , new Tuple2(3,4)
            , new Tuple2(3,6)));
    JavaRDD<Tuple2<Integer,Integer>> otherPre = sc.parallelize(Arrays.asList(new Tuple2(3,10)));

    //JavaRDD转换成JavaPairRDD
    JavaPairRDD<Integer, Integer> rdd = JavaPairRDD.fromJavaRDD(rddPre);
    JavaPairRDD<Integer, Integer> other = JavaPairRDD.fromJavaRDD(otherPre);
    //subtractByKey
    JavaPairRDD<Integer, Integer> subRDD = rdd.subtractByKey(other);

    //join
    JavaPairRDD<Integer, Tuple2<Float, Integer>> joinRDD =  rdd.join(other);

    //leftOuterJoin
    JavaPairRDD<Integer, Tuple2<Integer, Optional<Integer>>> integerTuple2JavaPairRDD = rdd.leftOuterJoin(other);

    //rightOutJoin
    JavaPairRDD<Integer, Tuple2<Optional<Integer>, Integer>> rightOutJoin = rdd.rightOuterJoin(other);