Get all key combinations from nested maps - scala

Question

I have a nested map like so:
val m: Map[Int, Map[String, Seq[Int]]] =
Map(
1 -> Map(
"A" -> Seq(1, 2, 3),
"B" -> Seq(4, 5, 6)
),
2 -> Map(
"C" -> Seq(7, 8, 9),
"D" -> Seq(10, 11, 12),
"E" -> Seq(13, 14, 15)
),
3 -> Map(
"F" -> Seq(16, 17, 18)
)
)
I want the desired output to show every possible combination of the integers in the Seqs. For example:
List((1, "A", 1),
(1, "A", 2),
(1, "A", 3),
(1, "B", 4),
(1, "B", 5),
(1, "B", 6),
(2, "C", 7),
(2, "C", 8),
(2, "C", 9),
(2, "D", 10),
(2, "D", 11),
(2, "D", 12),
(2, "E", 13),
(2, "E", 14),
(2, "E", 15),
(3, "F", 16),
(3, "F", 17),
(3, "F", 18))
I have been trying different combinations of map and flatMap, but nothing has been working. Any ideas?

Answer 1

Here is a possibility using a for comprehension:
for {
(k1, v1) <- m
(k2, v2) <- v1
v3 <- v2
} yield (k1, k2, v3)
This goes through all top key/value pairs of m. For each of these top values, this goes through all nested key/values. And finally for all of these nested values (which are the lists), it goes through each elements and yields what's requested.
A for comprehension is an equivalent to nested flatMaps, such as:
m.flatMap{
case (k1, v1) => v1.flatMap {
case (k2, v2) => v2.map(v3 => (k1, k2, v3))
}
}