I am working in Scala with java libraries. One of these libraries returns a list of lists. I want to flatten the list.
Example:
import scala.collection.JavaConverters._
var parentList : util.List[util.List[Int]] = null
parentList = new util.ArrayList[util.List[Int]]
parentList.asScala.flatten // error
I have used asScala converter but I'm still meeting an error.
You need to call .asScala on every inner list :
scala> parentList.asScala.map(_.asScala)
res0: scala.collection.mutable.Buffer[scala.collection.mutable.Buffer[Int]] = ArrayBuffer()
scala> parentList.asScala.map(_.asScala).flatten
res1: scala.collection.mutable.Buffer[Int] = ArrayBuffer()
Note that calling .map and then .flatten can be done in one step using .flatMap :
scala> parentList.asScala.flatMap(_.asScala)
res2: scala.collection.mutable.Buffer[Int] = ArrayBuffer()
You also need to convert the inner List[Int]:
parentList.asScala.flatMap(_.asScala)
Try like this
import scala.jdk.CollectionConverters._
parentList.asScala.flatMap.map(_.toSeq)
This will do the trick.
