Spark in Foreach - apache-spark

Question

val a = sc.textFile("/user/cts367689/datagen.txt")
val b = a.map(x => (x.split(",")(0),x.split(",")(2),x.split(4))))
val c = b.filter(x => (x._3.toInt > 500))
c.foreach(x => println(x))
or
c.foreach {x => {println(x)}}
I am not getting the expected output when i use for-each statement.I want output to be print one in a line but not sure what wrong in my code.

Answer 1

I think that this have been answered already a couple of times before but here we go again and from the Official Programming Guide :
Printing elements of an RDD
One common idiom is attempting to print out the elements of an RDD using rdd.foreach(println) or rdd.map(println). On a single machine, this will generate the expected output and print all the RDD’s elements.
scala> val rdd = sc.parallelize(Seq((1,2,3),(2,3,4)))
// rdd: org.apache.spark.rdd.RDD[(Int, Int, Int)] = ParallelCollectionRDD[0] at parallelize at <console>:27
scala> rdd.foreach(println)
// (1,2,3)
// (2,3,4)
However, in cluster mode, the output to stdout being called by the executors is now writing to the executor’s stdout instead, not the one on the driver, so stdout on the driver won’t show these!
To print all elements on the driver, one need to collect() the data back to the driver node thus:
scala> rdd.collect().foreach(println)
// (1,2,3)
// (2,3,4)
And here is the limitation. If your data doesn't fit on the driver, this can cause the driver to run out of memory, though, because collect() fetches the entire RDD to a single machine; Thus causing your driver to blow.
If you only need to print a few elements of the RDD, a safer approach is to use the take():
scala> val rdd = sc.parallelize(Range(1, 1000000000))
// rdd: org.apache.spark.rdd.RDD[Int] = ParallelCollectionRDD[2] at parallelize at <console>:27
scala> rdd.take(100).foreach(println)
// 1
// 2
// 3
// 4
// 5
// 6
// 7
// 8
// 9
// 10
// [...]
PS: A small note concerning the foreach method. foreach runs a function on each element of the dataset. This method is usually done for side effects such as updating an Accumulator or interacting with external storage systems.
I hope that this answers your question.