How to replace an Item in scala Map, keeping the order-CodePudding

I have a Map like this .

  val m1 = Map(1 -> "hello", 2 -> "hi", 3 -> "Good", 4 -> "bad")
  val m2 = Map(1 -> "Great", 3 -> "Guy")

Now I need to derive another Map from m1 and m2, and I need to replace elements of m1 by those m2 with order preserved.

m3 should like

   Map(1 -> "Great", 2 -> "hi",  3 -> "Guy", 4 -> "bad")

Is there a way to do it in functional programming??

CodePudding user response：

val m3 = m1    m2

However order is not preserved because Map is not ordered in the first place. If you want an ordered map use ListMap.

CodePudding user response：

Map does not preserve ordering. If you want to preserve insertion order use ListMap:

List map iterators and traversal methods visit key-value pairs in the order they were first inserted.

val m1 = ListMap(1 -> "hello", 2 -> "hi", 3 -> "Good", 4 -> "bad")
val m2 = Map(1 -> "Great", 3 -> "Guy")
val m3 = m1    m2

or SortedMap if you want ordering by the key:

An immutable map whose key-value pairs are sorted according to an scala.math.Ordering on the keys.