Combinations of Multiple Lists (Scala)

Question

I'm trying to write a function that takes multiple lists as input and returns a list of strings representation of every combination between those lists.

Sample Input:

val integers = List(1,2,3,4)
val characters = List('a','b','c')
val strings = List("apple","grapefruit")

Sample Output:

("1-a-apple", "1-a-grapefruit", .....)

Here is what I have so far:

def main(args: Array[String]): Unit = {
    
        val integers = List(1,2,3,4)
        val characters = List('a','b','c')
        val strings = List("apple","grapefruit")
    
        val lists = List(integers, characters, strings)
    
        println(generator(lists).toString())
    
      }
    
      //using list api
      def generator(x: List[List[Any]]): List[List[Any]] = x match {
        case Nil    => List(Nil)
        case h :: _ => h.flatMap(i => generator(x.tail).map(i :: _))
      }

And here is the output of my code:

List(List(1, a, apple), List(1, a, grapefruit), List(1, b, apple), List(1, b, grapefruit), List(1, c, apple), List(1, c, grapefruit), List(2, a, apple), List(2, a, grapefruit), List(2, b, apple), List(2, b, grapefruit), List(2, c, apple), List(2, c, grapefruit), List(3, a, apple), List(3, a, grapefruit), List(3, b, apple), List(3, b, grapefruit), List(3, c, apple), List(3, c, grapefruit), List(4, a, apple), List(4, a, grapefruit), List(4, b, apple), List(4, b, grapefruit), List(4, c, apple), List(4, c, grapefruit))

So my questions are:

1)How can I get the output to be a list of strings instead of list of list of any?

2)How can I use a for comprehension instead of the list api?

Answer 1

val integers = List(1,2,3,4)
val characters = List('a','b','c')
val strings = List("apple","grapefruit")

for {
  int <- integers
  chars <- characters
  string <- strings
} yield { s"${int}-${chars}-${string}" }

That code outputs

val res4: List[String] = List(1-a-apple, 1-a-grapefruit, 1-b-apple, 1-b-grapefruit, 1-c-apple, 1-c-grapefruit, 2-a-apple, 2-a-grapefruit, 2-b-apple, 2-b-grapefruit, 2-c-apple, 2-c-grapefruit, 3-a-apple, 3-a-grapefruit, 3-b-apple, 3-b-grapefruit, 3-c-apple, 3-c-grapefruit, 4-a-apple, 4-a-grapefruit, 4-b-apple, 4-b-grapefruit, 4-c-apple, 4-c-grapefruit)

Here's I'm using string interpolation (eg s" variable is $var1" ) to turn the items into strings.