sifting

demo.scala

scala> :load /home/eje/sift.scala
Loading /home/eje/sift.scala...
defined module sift
defined module demo

scala> import sift._
import sift._

scala> val r = Sifted.seq(demo.dirty).map(_.map(_.toDouble)).filter(_(0) > 1).map(_(1))
r: sift.SiftedSeq[Double,scala.collection.immutable.Vector,(scala.collection.immutable.Vector[scala.collection.immutable.Vector[Double]], (scala.collection.immutable.Vector[scala.collection.immutable.Vector[Double]], (scala.collection.immutable.Vector[scala.collection.immutable.Vector[String]], List[Nothing])))] = SiftedSeq(Vector(5.0),(Vector(Vector(3.0)),(Vector(Vector()),(Vector(Vector(2, 3, z)),List()))))

scala> r.passed
res0: scala.collection.immutable.Vector[Double] = Vector(5.0)

scala> r.retained
res1: (scala.collection.immutable.Vector[scala.collection.immutable.Vector[Double]], (scala.collection.immutable.Vector[scala.collection.immutable.Vector[Double]], (scala.collection.immutable.Vector[scala.collection.immutable.Vector[String]], List[Nothing]))) = (Vector(Vector(3.0)),(Vector(Vector()),(Vector(Vector(2, 3, z)),List())))

sift.scala

object sift {
  import scala.language.reflectiveCalls
  import scala.language.higherKinds
  import scala.language.implicitConversions  

  import scala.collection.SeqLike
  import scala.collection.generic.CanBuildFrom

  import scala.util.Either

  type Seive[T, U] = T => Either[T, U]

  def liftToSeive[T, U](f: T => U): Seive[T, U] = {
    (t: T) => try {
      Right(f(t))
    } catch {
      case _: Throwable => Left(t)
    }
  }

  case class SiftedSeq[T, S[E] <: SeqLike[E, S[E]], R](passed: S[T], retained: R) {
    def map[U](f: T => U)(implicit cbf1: CanBuildFrom[S[T], Either[T,U], S[Either[T,U]]], cbf2: CanBuildFrom[S[Either[T,U]], Either[T,U], S[Either[T,U]]], cbf3: CanBuildFrom[S[Either[T,U]], U, S[U]], cbf4: CanBuildFrom[S[Either[T,U]], T, S[T]]): SiftedSeq[U, S, (S[T], R)] = {
      val s = passed.map(liftToSeive(f))
      val p = s.filter(_.isRight).map(_.right.get)
      val r = s.filter(_.isLeft).map(_.left.get)
      SiftedSeq[U, S, (S[T], R)](p, (r, retained))
    }

    def filter(f: T => Boolean)(implicit cbf1: CanBuildFrom[S[T], T, S[T]]): SiftedSeq[T, S, (S[T], R)] = {
      val fs = liftToSeive(f)
      val p = passed.filter { e =>
        val t = fs(e)
        t.isRight && t.right.get
      }
      val r = passed.filter { e => fs(e).isLeft }
      SiftedSeq[T, S, (S[T], R)](p, (r, retained))
    }
  }

  object Sifted {
    def seq[T, S[E] <: SeqLike[E, S[E]]](data: S[T]) = SiftedSeq[T, S, List[Nothing]](data, Nil)
  }
}

object demo {
  val dirty = Vector(
    Vector("1", "2", "3"),
    Vector("2", "3", "z"),
    Vector(),
    Vector("3"),
    Vector("4", "5")
  )
}