I'm looking for a version of Expand a Set[Set[String]] into Cartesian Product in Scala based on map type :
I would like to start with :
val values = Map(
"id" -> List("Paul","Joe"),
"number" -> List("1","2","3"),
"Type" -> List("A","B","C")
)
And compute :
val final = Set(
Map("id" -> "Paul", "number" -> "1", "Type" -> "A" ),
Map("id" -> "Paul", "number" -> "1", "Type" -> "B" ),
Map("id" -> "Paul", "number" -> "1", "Type" -> "C" ),
Map("id" -> "Paul", "number" -> "1", "Type" -> "A" ),
Map("id" -> "Paul", "number" -> "1", "Type" -> "B" ),
Map("id" -> "Paul", "number" -> "1", "Type" -> "C" ),
Map("id" -> "Paul", "number" -> "2", "Type" -> "A" ),
Map("id" -> "Paul", "number" -> "2", "Type" -> "B" ),
Map("id" -> "Paul", "number" -> "2", "Type" -> "C" ),
....
Map("id" -> "Joe", "number" -> "3", "Type" -> "B" ),
Map("id" -> "Joe", "number" -> "3", "Type" -> "C" )
)
I try to transform the following code
def combine[A](xs: Traversable[Traversable[A]]): Seq[Seq[A]] =
xs.foldLeft(Seq(Seq.empty[A])){
(x, y) => for (a <- x.view; b <- y) yield a :+ b }
but I have some issue to understand how to construct all the map to add in the big Set()
You could do something like this:
(but note that for larger maps this would consume a lot of memory, it may be worth looking into generating a LazyList instead)
def cartesianProductMap[A, B](data: Map[A, List[B]]): List[Map[A, B]] =
data.foldLeft(Map.empty[A, B] :: Nil) {
case (acc, (key, values)) =>
values.flatMap { b =>
acc.map(_ + (key -> b))
}
}
Code running in Scastie.
BTW, if you use cats you could just do: values.to(SortedMap).sequence