Convert Map collection to List of Strings

Question

I'm trying to flatten a Map's contents to a List of Strings.

So this collection :

val d: scala.collection.immutable.Map[String, scala.collection.immutable.Seq[Any]] = 
  Map("b" -> List(Array(1.0, 2.0), 5.333333333333333),
      "d" -> List(Array(3.0, 3.0), 8.0))

Should be converted to a List[String] type of two elements :

  b,1,2,5.3
  d 3,3,8.0

To achieve this im attempting to decompose the map and flatten its keys using :

  d.map(m =>
  m match {
    case(k , v) => {
        (k , v.flatten)
    }
    })

But I receive error :

Multiple markers at this line - No implicit view available from Any => scala.collection.GenTraversableOnce[B]. - 
 not enough arguments for method flatten: (implicit asTraversable: Any => 
 scala.collection.GenTraversableOnce[B])scala.collection.immutable.Seq[B]. Unspecified value parameter 
 asTraversable.

How can collection scala.collection.immutable.Map[String, scala.collection.immutable.Seq[Any]] be converted to List[String] ?

Update :

This works : 

val map: Map[String, scala.collection.immutable.Seq[Any]] =
    Map(
      "bsds" -> List(Array(1.0, 2.0), 5.333333333333333),
      "dsdfsd" -> List(Array(3.0, 3.0), 8.0)
    )                                             //> map  : Map[String,scala.collection.immutable.Seq[Any]] = Map(bsds -> List(Ar
                                                  //| ray(1.0, 2.0), 5.333333333333333), dsdfsd -> List(Array(3.0, 3.0), 8.0))

  val flatten = map.map {
    case (k : String , v) =>
      val expanded = v map {
        case arr: Array[_] => Seq(arr: _*)
        case el : Double => Seq(el)
      }
      (k , (expanded.flatten))
  }                                               //> flatten  : scala.collection.immutable.Map[String,scala.collection.immutable.
                                                  //| Seq[Any]] = Map(bsds -> List(1.0, 2.0, 5.333333333333333), dsdfsd -> List(3.
                                                  //| 0, 3.0, 8.0))
  val ll = flatten.map(m => List(m._1) ++ m._2)   //> ll  : scala.collection.immutable.Iterable[List[Any]] = List(List(bsds, 1.0, 
                                                  //| 2.0, 5.333333333333333), List(dsdfsd, 3.0, 3.0, 8.0))
  ll.map(m => m.mkString("|"))                    //> res5: scala.collection.immutable.Iterable[String] = List(bsds|1.0|2.0|5.3333
                                                  //| 33333333333, dsdfsd|3.0|3.0|8.0)

@som-snytt I don't understand this question, how is tuple related to Seq[Any] ? — blue-sky, Sep 24 '14 at 21:34
Just that your example could be `Map[String, (Array[Double], Double)]`. Once you have Any, you don't know what's going on inside until it throws at runtime. — som-snytt, Sep 24 '14 at 22:10

score 1 · Accepted Answer · answered Sep 24 '14 at 19:26

1

  val map: Map[String, scala.collection.immutable.Seq[Any]] =
    Map(
      "b" -> List(Array(1.0, 2.0), 5.333333333333333),
      "d" -> List(Array(3.0, 3.0), 8.0)
    )

  val flatten = map.map {
    case (k, v) =>
      val expanded = v map {
        case arr: Array[_] => Seq(arr: _*)
        case el => Seq(el)
      }
      (k ++ expanded.flatten).mkString(",")
  }

  flatten.foreach(println)

answered Sep 24 '14 at 19:26

Eugene Zhulenev

9,714
2
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this line : Seq(arr: _*) what is this syntax computing "_*" ? – blue-sky Sep 24 '14 at 19:29
http://stackoverflow.com/questions/6051302/what-does-colon-underscore-star-do-in-scala – Eugene Zhulenev Sep 24 '14 at 19:38
I think this only works with one-char keys. `"abc" ++ Seq()` is not what you intended? – som-snytt Sep 24 '14 at 19:55
@som-snytt yes, it may also contain Strings, not just single characters – blue-sky Sep 24 '14 at 20:34

score 0 · Answer 2 · answered Sep 24 '14 at 20:05

Not as flat you want:

scala> import runtime.{ ScalaRunTime => RT }
import runtime.{ScalaRunTime=>RT}

scala> val m = Map("bcde" -> List(Array(1.0, 2.0), 5.333333333333333), "fghij" -> List(Array(3.0, 3.0), 8.0))
m: scala.collection.immutable.Map[String,List[Any]] = Map(bcde -> List(Array(1.0, 2.0), 5.333333333333333), fghij -> List(Array(3.0, 3.0), 8.0))

scala> m map { case (k,v) => s"${RT stringOf k}, ${v map (RT stringOf _) mkString ", "}" }
res7: scala.collection.immutable.Iterable[String] = List(bcde, Array(1.0, 2.0), 5.333333333333333, fghij, Array(3.0, 3.0), 8.0)

but worth advertising.

score 0 · Answer 3 · answered Oct 07 '14 at 03:53

0

Using a for comprehension, like this,

for ( (k, List(Array(a,b,_*),v)) <- d) yield Seq(k,a,b,v).mkString(",")

answered Oct 07 '14 at 03:53

elm

20,117
14
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Convert Map collection to List of Strings

3 Answers3