Scala: Partial function argument in collect api

The collect api in collection classes like Sequence uses a partial function as argument. The isDefinedAt mechanism of the partial function effectively acts as a filter for the incoming elements and the apply method acts as the transformer for the element.

Filter and map are fundamental operations in functional programming. My perspective on the collect api is as the hybrid of both together.

Let us take a demonstrative example of a sequence of numbers, only even numbers which need to be again doubled and returned. The way I would have approached is to have a filter to first filter in only the even numbers with a predicate like i % 2 ==0 , and then a map function to double the value like i => i * 2

val seqOne: Seq[Int] = Seq(1,2,3,4,5,6)
val resultOne = seqOne.filter(_%2==0).map(_*2)
println(resultOne)
List(4, 8, 12)

The equivalent collect approach would be as below

val doubleIfEven = new PartialFunction[Int,Int]  {
  def isDefinedAt(x : Int) = x % 2 == 0
  def apply(x : Int) = x * 2
}
val result = seqOne.collect(doubleIfEven)
println(result)
List(4, 8, 12)