Scala: Remove duplicates in list of objects

user_427079 0
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I've got a list of objects List[Object] which are all instantiated from the same class. This class has a field which must be unique Object.property. What is the cleanest way to iterate the list of objects and remove all objects(but the first) with the same property?

duplicates list scala
9 Answers

Starting Scala 2.13, most collections are now provided with a distinctBy method which returns all elements of the sequence ignoring the duplicates after applying a given transforming function:

list.distinctBy(_.property)

For instance:

List(("a", 2), ("b", 2), ("a", 5)).distinctBy(_._1) // List((a,2), (b,2))
List(("a", 2.7), ("b", 2.1), ("a", 5.4)).distinctBy(_._2.floor) // List((a,2.7), (a,5.4))
user_92971440

With a collection and a function from a record to a key this yields a list of records distinct by key. It's not clear whether groupBy will preserve the order in the original collection. It may even depend on the type of collection. I'm guessing either head or last will consistently yield the earliest element.

collection.groupBy(keyFunction).values.map(_.head)

When will Scala get a nubBy? It's been in Haskell for decades.

user_13476080

If you want to remove duplicates and preserve the order of the list you can try this two liner:

val tmpUniqueList = scala.collection.mutable.Set[String]()
val myUniqueObjects = for(o <- myObjects if tmpUniqueList.add(o.property)) yield o
user_12415400
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