Transform a list to a map - scala

Question

I have the following types:
case class Category(id: Int, name: String)
case class Product(id: Int, location: Location, categoryIdList: Option[List[Int]])
Given a list of products
val products:List[Product] = loadProducts()
How can I product a map of categoryId to Location?
Map[categoryId, Location]
So my method would look something like this:
def getMap(products: List[Product]): Map[Int, Location] = {
??
}
I need to somehow iterate over the optional list of categoryIdList and then create a map from that with the Location property.

Answer 1

In order to convert a Seq to a Map we need to first convert it to be a Seq[(Int,Location)], that is a Seq of a Tuple2. Only then will the toMap method actually be available.
Edit: Okay here's an implementation based on each categoryId on the list, note that you shouldn't use an option of a list, since an empty state for a List is just an empty list.
def getMap(products: List[Product]): Map[Int, Location] = {
products.flatMap(toListTuple2).toMap
}
def toListTuple2(product: Product): List[(Int, Location)] = {
product.categoryIdList
.getOrElse(List())
.map(category => (category, product.location))
}
So here we first turn our product into a list of categoryIds and Locations and then flatmap it to a List of (Int, Location), which can then be turned into a Map by calling toMap.

Answer 2

This should do what you are asking for however solution doesn't address problems provided in comments:
def getMap(products: List[Product]): Map[Int, Location] = {
val locations = scala.collection.mutable.Map[Int, Location]()
for {
product <- products
if product.categoryIdList.nonEmpty
category <- product.categoryIdList.get
} {
locations(category) = product.location
}
locations.toMap
}

Answer 3

def getMap(products: List[Product]) = {
products.map(p => (p.categoryIdList.getOrElse(List.empty), p.location))
.flatMap(x => x._1.map(_ -> x._2))
.toMap
}