CODEWITHSUNDEEP
scala
jcm
jcm

Reputation: 5659

How do I process this list of futures result

I have the following function:

def countAllFriends(currUser: String, members: List[String]): Future[Map[String, Integer]] = {
    val results: List[Future[List[String]]] = members.map(currUser => retrieveAllFriends( currUser))


    //go through the results, and return a future of a map of usernames to the number of times that username exists in the list


  }

How can I implement the function so that I get a return type of Future[Map[String, Integer]] ?

If a future fails, then I don't want the whole thing to fail, I just want to have a special entry in the map called 'failures' which will count the number of failed futures.

Upvotes: 1

Views: 1060

Answers (1)

Ende Neu
Ende Neu

Reputation: 15773

First use Future.sequence to get a Future[List[List[String]]:

val p: Future[List[List[String]]] = Future.sequence(results)

Then flatMap the future and the inner lists and use groupBy and map:

val g: Future[Map[String, Int]] = p.flatMap { listOfList =>
  Future(listOfList.flatten.groupBy(identity).map(maps => (maps._1, maps._2.length)))
}

Edit:

If you want to count the number of futures failed you could use this:

val futuresWithRecover: List[Future[List[String]]] = 
  results.map(f => f.map(identity).recover {case _ => List("failures") })

Then the process is the same:

val p: Future[List[List[String]]] = Future.sequence(futuresWithRecover)

val g: Future[Map[String, Int]] = p.flatMap { listOfList =>
  Future(listOfList.flatten.groupBy(identity).map(maps => (maps._1, maps._2.length)))
}

The second approach though is untested.

Upvotes: 3

Related Questions