How do I efficiently count distinct fields in a collection?

Question

I am currently doing this:

val count = sightings.map(_.shape).distinct.length

However,

map

creates an intermediary collection, which in my case is a Vector thousands of times larger than what

distinct

produces.

How do I bypass this intermediate step and get the set of distinct shapes? Or, even better, the count of distinct shapes.

Recommended for you: Get network issues from WhatsUp Gold. Not end users.

Answer 1

You can use an iterator to not create the intermediate collection and then accrue the shapes in a Set to get the distinct ones:

val count = sightings.iterator.map(_.shape).toSet.size

Alternatively, you can use collection.breakOut to accrue the items in a Set without creating the intermediate collection (another answer suggested using breakOut, but in a different way):

val distinctShapes: Set[Shape] = sightings.map(_.shape)(collection.breakOut)
val count = distinctShapes.size

How do I efficiently count distinct fields in a collection?

Sign up