How to find the last occurrence of an element in a Scala List?

As of Scala 2.13, you can use findLast to find the last element of a Seq satisfying a predicate, if one exists:

val students = List(Student(1, 23), Student(2, 24), Student(3, 23))
students.findLast(_.age == 23) // Option[Student] = Some(Student(3, 23))

I think maybe you can achieve this by filter with lastOption, like:

list.filter(student => student.age == 23).lastOption

chengpohi's and jwvh's answers work, but will traverse the list twice or more.

Here's a generic way to find the last occurence that will only traverse the list once:

def findLast[A](la: List[A])(f: A => Boolean): Option[A] =
  la.foldLeft(Option.empty[A]) { (acc, cur) => 
    if (f(cur)) Some(cur)
    else acc
  }

We walk through the collection exactly once and always take the last element that matches our predicate f.

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