原文作者:翟开顺
首发:CSDN
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原文地址:https://blog.csdn.net/t1dmzks/article/details/72077428
countByKey
def countByKey(): Map[K, Long]
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)}
scala例子
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scala> val rdd = sc.parallelize(Array((1, 2),(2,4),(2,5), (3, 4),(3,5), (3, 6)))
scala> val countbyKeyRDD = rdd.countByKey() countbyKeyRDD: scala.collection.Map[Int,Long] = Map(1 -> 1, 2 -> 2, 3 -> 3)
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java例子
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JavaRDD<Tuple2<Integer, Integer>> tupleRDD = 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> mapRDD = JavaPairRDD.fromJavaRDD(tupleRDD); Map<Integer, Object> countByKeyRDD = mapRDD.countByKey(); for (Integer i:countByKeyRDD.keySet()) { System.out.println("("+i+", "+countByKeyRDD.get(i)+")"); }
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collectAsMap
将pair类型(键值对类型)的RDD转换成map, 还是上面的例子
scala例子
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scala> val rdd = sc.parallelize(Array((1, 2),(2,4),(2,5), (3, 4),(3,5), (3, 6)))
scala> rdd.collectAsMap() res1: scala.collection.Map[Int,Int] = Map(2 -> 5, 1 -> 2, 3 -> 6)
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java例子
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JavaRDD<Tuple2<Integer, Integer>> tupleRDD = 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> mapRDD = JavaPairRDD.fromJavaRDD(tupleRDD);
Map<Integer, Integer> collectMap = mapRDD.collectAsMap();
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