Scala Breeze zipValues issue

Question

Say I have the following Scala code. I am running Scala 2.11.8 and Breeze 0.13.

val a: DenseVector[Double] = DenseVector(1.1, 1.2, 1.3)
val b: DenseVector[Double] = DenseVector(1.1, 1.2, 1.3)

val v: DenseVector[Double] = zipValues(a, b) ((ai: Double, bi: Double) => ai + bi)

I get a type mismatch compilation error which gets translated to:

[error] /Users/luishreis/Documents/projects/scala/sbt/GA/src/main/scala/ga_class.scala:119: type mismatch;
[error]  found   : (Double, Double) => Double
[error]  required:     breeze.linalg.zipValues.Impl2[breeze.linalg.DenseVector[Double],breeze.linalg.DenseVector[Double],?]
[error]     (which expands to)  breeze.generic.UFunc.UImpl2[breeze.linalg.zipValues.type,breeze.linalg.DenseVector[Double],breeze.linalg.DenseVector[Double],?]
[error]     val v: DenseVector[Double] = zipValues(a, b) ((ai: Double, bi: Double) => ai + bi)

I have tried with different types and such, but no success. Anyone care to shine a light on the inner workings of zipValue? Any help would be apreciated.

Answer 1

If you search the repository for zipValues, you'll see it's normally used as zipValues(a, b).foreach(...). Your case would probably need zipValues(a, b).map((ai, bi) => ai + bi), but unfortunately, it isn't currently defined:

/**
 * Usually used as the return type from zipValues
 * @tparam V1
 * @tparam V2
 */
trait ZippedValues[@specialized(Double) V1, @specialized(Double) V2] {
  def foreach(f: (V1,V2) => Unit)

  def exists(f: (V1, V2)=>Boolean):Boolean = {
    foreach((a,b) => if (f(a,b)) return true)
    false
  }

  def forall(f: (V1, V2)=>Boolean):Boolean = {
    foreach((a,b) => if (!f(a,b)) return false)
    true
  }
  // TODO: define map for this.
//  def map[A](a: Coll1, b: Coll2, f: (V1,V2)=>A)(implicit canZipMapValues)
}