Behavior of groupBy().mapValues() differs in Scala 2.12 vs Scala 2.13

Question
1

Hi,

I observed a difference in behavior with the following piece of code in Scala 2.12 vs Scala 2.13:

object Solution {
  def groupAnagrams(strs: Array[String]): List[List[String]] = {
    val groups = strs.groupBy(str => str.groupBy(identity).mapValues(_.length))
    groups.map(_._2.toList).toList
  }

  def main(args: Array[String]): Unit = {
    println(groupAnagrams(Array("eat","tea","tan","ate","nat","bat")))
  }
}

Here the creation of groups use a Map as the key, this produces the following output in Scala 2.12.15:

List(List(eat, tea, ate), List(tan, nat), List(bat))

and the following output in Scala 2.13.7:

List(List(ate), List(tea), List(eat), List(bat), List(nat), List(tan))

I assume this is due to the MapView that is returned by the mapValues function.
Just wanted to confirm if this behavior is expected.

Thanks,
Krishna Rajendram Bashyam.

2

Note that mapValues is deprecated in 2.13.

When I compile your code, the deprecation warning tells me:

warning: method mapValues in trait MapOps is deprecated (since 2.13.0): Use .view.mapValues(f). A future version will include a strict version of this method (for now, .view.mapValues(f).toMap).

2 Likes
3

It’s a pity that this was not changed in Scala 3. Since moving from Scala 2.13 to 3.0 is some work after all, this would have not added much. (There are a few more of these cases, if i remember correctly). In Scala 3.1.3 i still get this warning.

4

To aid migration, Scala 3.0 uses 2.13’s standard library unaltered. Eventually we’ll be free to start changing it again.

2 Likes
5

eventually
eventually1902×1573 293 KB

3 Likes