Hi Jeff, > But in our development environment, the returned RDD results were empty and > b.function(_) was never executed what do you mean by "the returned RDD results were empty", did you try running a foreach, collect or any other action on the returned RDD[C]?
Spark provides two kinds of operations on RDDs: 1. transformations, which return a new RDD and are lazy and 2. actions that actually run an RDD and return some kind of result. In your example above, 'map' is a transformation and thus is not actually applied until some action (like 'foreach') is called on the resulting RDD. You can find more information in the Spark Programming Guide http://spark.apache.org/docs/latest/programming-guide.html#rdd-operations. best, --Jakob On Tue, Mar 8, 2016 at 5:41 PM, Hemminger Jeff <j...@atware.co.jp> wrote: > > I'm currently developing a Spark Streaming application. > > I have a function that receives an RDD and an object instance as a > parameter, and returns an RDD: > > def doTheThing(a: RDD[A], b: B): RDD[C] > > > Within the function, I do some processing within a map of the RDD. > Like this: > > > def doTheThing(a: RDD[A], b: B): RDD[C] { > > a.combineByKey(...).map(b.function(_)) > > } > > > I combine the RDD by key, then map the results calling a function of > instance b, and return the results. > > Here is where I ran into trouble. > > In a unit test running Spark in memory, I was able to convince myself that > this worked well. > > But in our development environment, the returned RDD results were empty and > b.function(_) was never executed. > > However, when I added an otherwise useless foreach: > > > doTheThing(a: RDD[A], b: B): RDD[C] { > > val results = a.combineByKey(...).map(b.function(_)) > > results.foreach( p => p ) > > results > > } > > > Then it works. > > So, basically, adding an extra foreach iteration appears to cause > b.function(_) to execute and returns results correctly. > > I find this confusing. Can anyone shed some light on why this would be? > > Thank you, > Jeff > > > --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@spark.apache.org For additional commands, e-mail: user-h...@spark.apache.org
