Scala：将地图大小n拆分为列表（地图最大尺寸3）

Question

In:

Map("k1" -> "v1", "k2" -> "v2", "k3" -> "v3", "k4" -> "v4", "k5" -> "v5", "k6" -> "v6", "k7" -> "v7", "k8" -> "v8", "k9" -> "v9", "k0" -> "v0")

Out:

List(Map("k1" -> "v1", "k2" -> "v2", "k3" -> "v3), Map("k4" -> "v4", "k5" -> "v5", "k6" -> "v6), Map("k7" -> "v7", "k8" -> "v8", "k9" -> "v9), Map("k0" -> "v0"))

Answer 1

val a = Map("k1" -> "v1", "k2" -> "v2", "k3" -> "v3", "k4" -> "v4", "k5" -> "v5", "k6" -> "v6", "k7" -> "v7", "k8" -> "v8", "k9" -> "v9", "k0" -> "v0")
a.grouped(3).toList

This gives you:

res2: List[scala.collection.immutable.Map[String,String]] = List(Map(k2 -> v2, k0 -> v0, k5 -> v5), Map(k9 -> v9, k6 -> v6, k7 -> v7), Map(k1 -> v1, k4 -> v4, k3 -> v3), Map(k8 -> v8))

The only thing it's not ordered

To keep the order you can do something like this:

a.toList.sortBy(_._1).grouped(3).toList.map(_.toMap)

Which gives you:

res6: List[scala.collection.immutable.Map[String,String]] = List(Map(k0 -> v0, k1 -> v1, k2 -> v2), Map(k3 -> v3, k4 -> v4, k5 -> v5), Map(k6 -> v6, k7 -> v7, k8 -> v8), Map(k9 -> v9))

Note that your initial Map is not sorted properly (the last element is "k0", but it should be the first one). But if you want to keep the insertion order and have the list of maps grouped by 3 this one should work:

val b = scala.collection.mutable.LinkedHashMap("k1" -> "v1", "k2" -> "v2", "k3" -> "v3", "k4" -> "v4", "k5" -> "v5", "k6" -> "v6", "k7" -> "v7", "k8" -> "v8", "k9" -> "v9", "k0" -> "v0")
b.toList.grouped(3).toList.map(_.toMap)

This results to:

res8: List[scala.collection.immutable.Map[String,String]] = List(Map(k1 -> v1, k2 -> v2, k3 -> v3), Map(k4 -> v4, k5 -> v5, k6 -> v6), Map(k7 -> v7, k8 -> v8, k9 -> v9), Map(k0 -> v0))