Newbie Scala question about simple math array operations

Question

Newbie Scala Question:

Say I want to do this [Java code] in Scala:

public static double[] abs(double[] r, double[] im) {
  double t[] = new double[r.leng         


        

Answer 1

Use zip and map:

scala> val reals = List(1.0, 2.0, 3.0)
reals: List[Double] = List(1.0, 2.0, 3.0)

scala> val imags = List(1.5, 2.5, 3.5)
imags: List[Double] = List(1.5, 2.5, 3.5)

scala> reals zip imags
res0: List[(Double, Double)] = List((1.0,1.5), (2.0,2.5), (3.0,3.5))

scala> (reals zip imags).map {z => math.sqrt(z._1*z._1 + z._2*z._2)}
res2: List[Double] = List(1.8027756377319946, 3.2015621187164243, 4.6097722286464435)

scala> def abs(reals: List[Double], imags: List[Double]): List[Double] =
     | (reals zip imags).map {z => math.sqrt(z._1*z._1 + z._2*z._2)}
abs: (reals: List[Double],imags: List[Double])List[Double]

scala> abs(reals, imags)
res3: List[Double] = List(1.8027756377319946, 3.2015621187164243, 4.6097722286464435)

UPDATE

It is better to use zipped because it avoids creating a temporary collection:

scala> def abs(reals: List[Double], imags: List[Double]): List[Double] =
     | (reals, imags).zipped.map {(x, y) => math.sqrt(x*x + y*y)}
abs: (reals: List[Double],imags: List[Double])List[Double]

scala> abs(reals, imags)
res7: List[Double] = List(1.8027756377319946, 3.2015621187164243, 4.6097722286464435)