24 November 2015

countByValue() Example

countByValue() is an action that returns the Map of each unique value with its count

def countByValue()(implicit ord: Ordering[T] = null): Map[T, Long]
Return the count of each unique value in this RDD as a local map of (value, count) pairs.

Note that this method should only be used if the resulting map is expected to be small, as the whole thing is loaded into the driver's memory. To handle very large results, consider using rdd.map(x => (x, 1L)).reduceByKey(_ + _), which returns an RDD[T, Long] instead of a map.

scala> val inputrdd = sc.parallelize{ Seq(10, 4, 3, 3) }
inputrdd: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[28] at parallelize at :47

scala> inputrdd.countByValue()
res34: scala.collection.Map[Int,Long] = Map(10 -> 1, 3 -> 2, 4 -> 1)


Learning Spark : 41