collections

Scala Set FAQ: How do I create a mutable Set in Scala?

To create a mutable set in Scala, first determine the type of set you want. You do this because the mutable Set is actually a trait, and you need to determine which concrete implementation you want.

For instance, if you want a SortedSet of String, define it like this:

val names = scala.collection.mutable.SortedSet[String]()

Then you can add elements to the set later like this:

Scala flatMap FAQ: Can you share some Scala flatMap examples?

Sure. When I was first trying to learn Scala, and cram the collections' flatMap method into my brain, I scoured books and the internet for great flatMap examples. Once I had a little grasp of it I started creating my own examples, and tried to keep them simple.

Using flatMap on a list of String

The following examples show the differences between map and flatMap on a sequence of String:

A cool thing about Scala sets -- and some other Scala collections -- is that you can easily determine the union, intersection, and difference between two sets. The following examples demonstrate how the methods work. First, we create two sets that have a slight overlap:

scala> val low = 1 to 5 toSet
low: scala.collection.immutable.Set[Int] = Set(5, 1, 2, 3, 4)

scala> val medium = (3 to 7).toSet
medium: scala.collection.immutable.Set[Int] = Set(5, 6, 7, 3, 4)

Now we exercise the methods. First, the union:

If you ever want to have a little fun with Scala, try experimenting with the Scala parallel collections. The following example gives you a little idea of what can happen in the most simple case of creating and using a parallel collection:

Wow, I began by writing a few Scala programming tutorials just because I like the language, and as I look here a couple of months later I now have more than sixty tutorials. As a result, I thought I'd start organizing them here in the form a Scala Programming Cookbook.

Here's my current collection of Scala FAQs and recipes, in a "cookbook" format.