[jira] [Created] (FLINK-8828) Add collect method to DataStream / DataSet scala api

["Jelmer Kuperus (JIRA)" <ji...@apache.org>]

Jelmer Kuperus created FLINK-8828:
-------------------------------------

             Summary: Add collect method to DataStream / DataSet scala api
                 Key: FLINK-8828
                 URL: https://issues.apache.org/jira/browse/FLINK-8828
             Project: Flink
          Issue Type: Improvement
          Components: Core, DataSet API, DataStream API, Scala API
    Affects Versions: 1.4.0
            Reporter: Jelmer Kuperus


A collect function is a method that takes a Partial Function as its parameter and applies it to all the elements in the collection to create a new collection which satisfies the Partial Function.

It can be found on all [core scala collection classes|http://www.scala-lang.org/api/2.9.2/scala/collection/TraversableLike.html] as well as on spark's [rdd interface|https://spark.apache.org/docs/2.2.0/api/scala/index.html#org.apache.spark.rdd.RDD]

To understand its utility imagine the following scenario :(

You have a DataStream that produces events of type _Purchase_ and View 
You would like to transform this stream into a stream of purchase amounts over 1000 euros. 

Currently an implementation might look like
{noformat}
val x = dataStream
  .filter(_.isInstanceOf[Purchase])
  .map(_.asInstanceOf[Purchase])
  .filter(_.amount > 1000)
  .map(_.amount){noformat}
Or alternatively you could do this
{noformat}
dataStream.flatMap(_ match {
  case p: Purchase if p.amount > 1000 => Some(p.amount)
  case _ => None
}){noformat}
But with collect implemented it could look like
{noformat}
dataStream.collect {
  case p: Purchase if p.amount > 1000 => p.amount
}{noformat}
 

Which is a lot nicer to both read and write



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