问题描述
我正在寻找基于地图类型的 Expand a Set[Set[String]] into Cartesian Product in Scala 版本:
我想开始:
val values = Map(
"id" -> List("Paul","Joe"),"number" -> List("1","2","3"),"Type" -> List("A","B","C")
)
并计算:
val final = Set(
Map("id" -> "Paul","number" -> "1","Type" -> "A" ),Map("id" -> "Paul","Type" -> "B" ),"Type" -> "C" ),"number" -> "2",....
Map("id" -> "Joe","number" -> "3",Map("id" -> "Joe","Type" -> "C" )
)
我尝试转换以下代码
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 }
但我有一些问题要理解如何构造所有地图以添加到大 Set() 中
解决方法
你可以这样做:
(但请注意,对于较大的地图,这会消耗大量内存,因此可能值得考虑生成一个 LazyList)
sample(x[!is.na(x)],1)
在 Scastie 中运行的代码。
顺便说一句,如果你使用cats,你可以这样做: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))
}
}