Convert List of tuple to map (and deal with duplicate key ?)

Question

I was thinking about a nice way to convert a List of tuple with duplicate key [(\"a\",\"b\"),(\"c\",\"d\"),(\"a\",\"f\")] into map (\"a\" -> [\"b\", \"

Answer 1

For Googlers that do care about duplicates:

implicit class Pairs[A, B](p: List[(A, B)]) {
  def toMultiMap: Map[A, List[B]] = p.groupBy(_._1).mapValues(_.map(_._2))
}

> List("a" -> "b", "a" -> "c", "d" -> "e").toMultiMap
> Map("a" -> List("b", "c"), "d" -> List("e"))