一、countByKey
以RDD{(1, 2),(2,4),(2,5), (3, 4),(3,5), (3, 6)}为例 rdd.countByKey会返回{(1,1),(2,2),(3,3)}即1个以1为key,2个以2为key,3个以3为key
scala版本
val rdd = sc.makeRDD(List((1,2),(2,4),(2,5),(3,4),(3,5),(3,6)))
rdd.countByKey.foreach(println) //(1,1) (2,2) (3,3)
java版本
JavaRDD<Tuple2<Integer,Integer>> rdd
=sc.parallelize(Arrays.asList(new Tuple2<>(1,2),new Tuple2<>(2,4),new Tuple2<>(2,5),
new Tuple2<>(3,4),new Tuple2<>(3,5),new Tuple2<>(3,6)));
JavaPairRDD<Integer, Integer> pairRDD = JavaPairRDD.fromJavaRDD(rdd);
Map<Integer, Long> map = pairRDD.countByKey();
Set<Integer> keys = map.keySet();
for (Integer i : keys) {
System.out.println(i+","+map.get(i));
}
二、collectAsMap
将pair类型(键值对类型)的RDD转换成map
注:同一个key,value的值会覆盖
scala版本
val rdd = sc.makeRDD(List((1,2),(2,4),(2,5),(3,4),(3,5),(3,6)))
rdd.collectAsMap.foreach(println) //(1,2) (2,5) (3,6)
java版本
JavaRDD<Tuple2<Integer,Integer>> rdd
=sc.parallelize(Arrays.asList(new Tuple2<>(1,2),new Tuple2<>(2,4),new Tuple2<>(2,5),
new Tuple2<>(3,4),new Tuple2<>(3,5),new Tuple2<>(3,6)));
JavaPairRDD<Integer, Integer> pairRdd = JavaPairRDD.fromJavaRDD(rdd);
Map<Integer, Integer> map = pairRdd.collectAsMap();
Set<Integer> keys = map.keySet();
for (Integer key :keys) {
System.out.println(key+","+map.get(key));
}