Sample code to find the windowed max in a series of numbers

windowed-max-sample.scala

import org.scalatest.{Matchers, WordSpec}


object SeqOps {

  // Adds windowing operations to sequences
  implicit class WindowOps[A](val seq: Seq[A]) extends AnyVal {

    def windowedMax[T, X](window: T)(t: A => T, x: A => X)(implicit numeric: Numeric[T], ordering: Ordering[X]): Seq[A] =
      seq.tail.scanLeft(Seq(seq.head)) { case (s, cur) =>
        val tmin = numeric.minus(t(cur), window)
        val nonExpired = s.dropWhile(e => numeric.lteq(t(e), tmin))
        val greater = nonExpired.takeWhile(e => ordering.gt(x(e), x(cur)))

        greater :+ cur

      }.map(_.head)
  }

}

class GeminiProbSpec extends WordSpec with Matchers {
  import SeqOps._

  case class Element(t: Int, x: Int)

  "windowedMax" should {

    "find max in ascending sequence" in {
      val input = (0 to 5).map(i => Element(i, i)).toSeq
      val expected = (0 to 5).map(i => Element(i, i)).toSeq

      input.windowedMax(3)(_.t, _.x) shouldBe expected
    }

    "find max in descending sequence" in {
      val input = (10 to 0 by -1).map(i => Element(10 - i, i)).toSeq
      val expected = Seq.fill(3)(Element(0, 10)) ++ (1 to 8).map(i => Element(i, 10 - i))

      input.windowedMax(3)(_.t, _.x) shouldBe expected
    }
    
    // TODO: Test cyclic and repetitive data sets

  }

}