Benchmark for performance of .toSet

SetPerformance.scala

package set.performance

import java.util.concurrent.TimeUnit

import scala.concurrent.duration.FiniteDuration

/**
* On my machine the fast method takes < 2 ms, the slow one 2.2s
*/
object SetPerformance {
  val keys: Set[Int] = Set(1, 2, 3)

  val map: Map[Int, Int] = (0 until 10000).map(x ⇒ (x, x)).toMap

  val iterations = 10000

  val testLoops = 10

  def main(args: Array[String]): Unit = (1 to testLoops).foreach{ iteration ⇒
    println(s"Running slow $iteration")
    println(time(slow()))

    println(s"Running fast $iteration")
    println(time(fast()))
    println()
  }

  private def slow() =
    (0 until iterations) foreach { _ ⇒
      // everything up to the toSet is very fast (comment the toSet out to see)
      // the problem is toSet
      map.filterKeys(keys).values.toSet
    }

  private def fast() =
    (0 until iterations) foreach { _ ⇒
      keys.flatMap(map.get)
    }

  def time[T](f: ⇒ T): FiniteDuration = {
    val start = System.currentTimeMillis()
    f
    val end = System.currentTimeMillis()
    FiniteDuration(end - start, TimeUnit.MILLISECONDS)
  }
}