# Ordering, a Scala language concept

Last updated

In Scala, the 'Ordering' type is a 'type class' that contains methods to determine an ordering of specific types.

``````assert(List(3, 2, 1).sorted == List(1, 2, 3))

assert(List(3, 2, 1).sorted(Ordering[Int].reverse) == List(3, 2, 1))

assert(Ordering[Int].lt(1, 2))

assert(!Ordering[Int].lt(2, 1))
``````

### Custom orderings can be created and composed

The 'Ordering' type class is very powerful because complex orderings can be achieved from small parts, and they can even be context-specific.

``````final case class Person(name: String, height: Int)

val people: List[Person] = List(
Person("Ann", height = 176),
Person("Thomas", height = 175),
Person("Judy", height = 173)
)

implicit val personOrdering: Ordering[Person] =
Ordering.by((_: Person).height)

assert(people.sorted.map(_.name) == List("Judy", "Thomas", "Ann"))

assert(people.sortBy(_.name).map(_.name) == List("Ann", "Judy", "Thomas"))

people.sortBy(person => (person.height, person.name))
``````

# Scala Algorithms: The most comprehensive library of algorithms in standard pure-functional Scala

## How our 100 algorithms look

1. A description/goal of the algorithm.
2. An explanation with both Scala and logical parts.
3. A proof or a derivation, where appropriate.
4. Links to Scala concepts used in this specific algorithm, also unit-tested.
5. An implementation in pure-functional immutable Scala, with efficiency in mind (for most algorithms, this is for paid subscribers only).
6. Unit tests, with a button to run them immediately in our in-browser IDE.

### Study our 100 Scala Algorithms: 6 fully free, 100 published & 0 upcoming

Fully unit-tested, with explanations and relevant concepts; new algorithms published about once a week.

### Explore the 22 most useful Scala concepts

To save you going through various tutorials, we cherry-picked the most useful Scala concepts in a consistent form.

## Subscribe to Scala Algorithms

Maximize your Scala with disciplined and consistently unit-tested solutions to 100+ algorithms.

Use it from improving your day-to-day data structures and Scala; all the way to interviewing.