Question

Consider the following structure (in reality the structure is a bit more complex):

case class A(id:String,name:String) {
   override def equals(obj: Any):Boolean = {
      if (obj == null || !obj.isInstanceOf[A]) return false
      val a = obj.asInstanceOf[A]
      name == a.name
   }

   override def hashCode() = {
      31 + name.hashCode
   }
}

val a1 = A("1","a")
val a2 = A("2","a")
val a3 = A("3","b")
val list = List((a1,a2),(a1,a3),(a2,a3))

Now let’s say I want to group all tuples with equal A’s. I could implement it like this

list.groupBy {
  case (x,y) => (x,y)
}

But, I don’t like to use pattern matching here, because it’s not adding anything here. I want something simple, like this:

list.groupBy(_)

Unfortunately, this doesn’t compile. Not even when I do:

list.groupBy[(A,A)](_)

Any suggestions how to simplify my code?

Answer 1

list.groupBy { case (x,y) => (x,y) }

Here you are deconstructing the tuple into its two constituent parts, just to immediately reassemble them exactly like they were before. In other words: you aren’t actually doing anything useful. The input and output are identical. This is just the same as

list.groupBy { t => t }

which is of course just the identity function, which Scala helpfully provides for us:

list groupBy identity