scala-collection-plus

A few extras to handle Scala 2.13's deprecation of .mapValues()

I'm just a developer, standing in front of a Scala v2.13 Map, asking it to map its values.

import com.madgag.scala.collection.decorators._

mapV

A concise replacement for mapValues(), that generates immutable Maps and avoids the verbose .view.mapValues(f).toMap syntax that becomes necessary in Scala 2.13:

val m = Map("foo" -> 5, "bar" -> 10)
// m: Map[String, Int] = Map("foo" -> 5, "bar" -> 10)
def f(i: Int) = i + 1

m.transform{case(_,v)=>f(v)}
// res0: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)
m.view.mapValues(f).toMap
// res1: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)
m.mapValues(f)
// res2: collection.MapView[String, Int] = MapView(("foo", 6), ("bar", 11))
m.mapV(f)                    
// res3: Map[String, Int] = Map("foo" -> 6, "bar" -> 11)

groupUp

Scala 2.13 introduced groupMap & groupMapReduce (see original GitHub Issue & PR) which potentially are another way to avoid the verbosity of mapValues in Scala 2.13. In the codebase I'm working on, there were unfortunately only a few examples where they were applicable.

There were more than twice as many opportunities to use a new groupUp(k)(g) method, equivalent to s.groupBy(k).view.mapValues(g).toMap - the difference is that while groupMap requires you to map over the individual elements in each collection that forms a value in the Map, groupUp instead allows you to perform any operation (not just map) that you might want. In the codebase I'm working on, that turns out to be more useful.

val s = Seq("foo", "foo", "bar", "bang")
// s: Seq[String] = List("foo", "foo", "bar", "bang")
def k(str: String) = str.length
def g(strs: Seq[String]) = strs.size

s.groupBy(k).view.mapValues(g).toMap // Scala 2.13 syntax
// res4: Map[Int, Int] = Map(3 -> 3, 4 -> 1) // Scala 2.13 syntax
s.groupBy(k).mapValues(g)            // deprecated in Scala 2.13, now returns MapView[K,B]
// res5: collection.MapView[Int, Int] = MapView((3, 3), (4, 1))            // deprecated in Scala 2.13, now returns MapView[K,B]
s.groupUp(k)(g)                      // provided by scala-213-collections-plus
// res6: Map[Int, Int] = Map(3 -> 3, 4 -> 1)