Ordering

@implicitNotFound(msg = "No implicit Ordering defined for ${T}.") trait Ordering[T] extends Comparator[T] with PartialOrdering[T] with Serializable

Ordering is a trait whose instances each represent a strategy for sorting instances of a type.

Ordering's companion object defines many implicit objects to deal with subtypes of AnyVal (e.g. Int, Double), String, and others.

To sort instances by one or more member variables, you can take advantage of these built-in orderings using Ordering.by and Ordering.on:

import scala.util.Sorting val pairs = Array(("a", 5, 2), ("c", 3, 1), ("b", 1, 3)) // sort by 2nd element Sorting.quickSort(pairs)(Ordering.by[(String, Int, Int), Int](_._2)) // sort by the 3rd element, then 1st Sorting.quickSort(pairs)(Ordering[(Int, String)].on(x => (x._3, x._1)))

An Ordering[T] is implemented by specifying compare(a:T, b:T), which decides how to order two instances a and b. Instances of Ordering[T] can be used by things like scala.util.Sorting to sort collections like Array[T].

For example:

import scala.util.Sorting case class Person(name:String, age:Int) val people = Array(Person("bob", 30), Person("ann", 32), Person("carl", 19)) // sort by age object AgeOrdering extends Ordering[Person] { def compare(a:Person, b:Person) = a.age compare b.age } Sorting.quickSort(people)(AgeOrdering)

This trait and scala.math.Ordered both provide this same functionality, but in different ways. A type T can be given a single way to order itself by extending Ordered. Using Ordering, this same type may be sorted in many other ways. Ordered and Ordering both provide implicits allowing them to be used interchangeably.

You can import scala.math.Ordering.Implicits to gain access to other implicit orderings.

trait Equiv[T]
trait Comparator[T]
class Object
trait Matchable
class Any

Type members

Classlikes

class OrderingOps(lhs: T)
Implicitly added by Option

This inner class defines comparison operators available for T.

It can't extend AnyVal because it is not a top-level class or a member of a statically accessible object.

class OrderingOps(lhs: T)
Implicitly added by Iterable

This inner class defines comparison operators available for T.

It can't extend AnyVal because it is not a top-level class or a member of a statically accessible object.

class OrderingOps(lhs: T)

This inner class defines comparison operators available for T.

It can't extend AnyVal because it is not a top-level class or a member of a statically accessible object.

Value members

Abstract methods

def compare(x: T, y: T): Int
Implicitly added by Option

Returns an integer whose sign communicates how x compares to y.

The result sign has the following meaning:

- negative if x < y - positive if x > y - zero otherwise (if x == y)

def compare(x: T, y: T): Int
Implicitly added by Iterable

Returns an integer whose sign communicates how x compares to y.

The result sign has the following meaning:

- negative if x < y - positive if x > y - zero otherwise (if x == y)

def compare(x: T, y: T): Int

Returns an integer whose sign communicates how x compares to y.

The result sign has the following meaning:

- negative if x < y - positive if x > y - zero otherwise (if x == y)

Concrete methods

override def equiv(x: T, y: T): Boolean

Return true if x == y in the ordering.

Definition Classes
Source
Ordering.scala
override def gt(x: T, y: T): Boolean

Return true if x > y in the ordering.

Definition Classes
Source
Ordering.scala
override def gteq(x: T, y: T): Boolean

Return true if x >= y in the ordering.

Definition Classes
Source
Ordering.scala
def isReverseOf(other: Ordering[_]): Boolean
Implicitly added by Option

Returns whether or not the other ordering is the opposite ordering of this one.

Equivalent to other == this.reverse.

Implementations should only override this method if they are overriding reverse as well.

def isReverseOf(other: Ordering[_]): Boolean
Implicitly added by Iterable

Returns whether or not the other ordering is the opposite ordering of this one.

Equivalent to other == this.reverse.

Implementations should only override this method if they are overriding reverse as well.

def isReverseOf(other: Ordering[_]): Boolean

Returns whether or not the other ordering is the opposite ordering of this one.

Equivalent to other == this.reverse.

Implementations should only override this method if they are overriding reverse as well.

override def lt(x: T, y: T): Boolean

Return true if x < y in the ordering.

Definition Classes
Source
Ordering.scala
override def lteq(x: T, y: T): Boolean

Return true if x <= y in the ordering.

Definition Classes
Source
Ordering.scala
def max[U <: T](x: U, y: U): U
Implicitly added by Option

Return x if x >= y, otherwise y.

def max[U <: T](x: U, y: U): U
Implicitly added by Iterable

Return x if x >= y, otherwise y.

def max[U <: T](x: U, y: U): U

Return x if x >= y, otherwise y.

def min[U <: T](x: U, y: U): U
Implicitly added by Option

Return x if x <= y, otherwise y.

def min[U <: T](x: U, y: U): U
Implicitly added by Iterable

Return x if x <= y, otherwise y.

def min[U <: T](x: U, y: U): U

Return x if x <= y, otherwise y.

def on[U](f: U => T): Ordering[U]
Implicitly added by Option

Given f, a function from U into T, creates an Ordering[U] whose compare function is equivalent to:

def compare(x:U, y:U) = Ordering[T].compare(f(x), f(y))
def on[U](f: U => T): Ordering[U]
Implicitly added by Iterable

Given f, a function from U into T, creates an Ordering[U] whose compare function is equivalent to:

def compare(x:U, y:U) = Ordering[T].compare(f(x), f(y))
def on[U](f: U => T): Ordering[U]

Given f, a function from U into T, creates an Ordering[U] whose compare function is equivalent to:

def compare(x:U, y:U) = Ordering[T].compare(f(x), f(y))
def orElse(other: Ordering[T]): Ordering[T]
Implicitly added by Option

Creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else the result of others compare function.

Value Params
other

an Ordering to use if this Ordering returns zero

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElse(Ordering.by[Pair, Int](_.b))
Source
Ordering.scala
def orElse(other: Ordering[T]): Ordering[T]
Implicitly added by Iterable

Creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else the result of others compare function.

Value Params
other

an Ordering to use if this Ordering returns zero

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElse(Ordering.by[Pair, Int](_.b))
Source
Ordering.scala
def orElse(other: Ordering[T]): Ordering[T]

Creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else the result of others compare function.

Value Params
other

an Ordering to use if this Ordering returns zero

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElse(Ordering.by[Pair, Int](_.b))
Source
Ordering.scala
def orElseBy[S](f: T => S)(ord: Ordering[S]): Ordering[T]
Implicitly added by Option

Given f, a function from T into S, creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else a result equivalent to:

Ordering[S].compare(f(x), f(y))

This function is equivalent to passing the result of Ordering.by(f) to orElse.

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElseBy[Int](_.b)
Source
Ordering.scala
def orElseBy[S](f: T => S)(ord: Ordering[S]): Ordering[T]
Implicitly added by Iterable

Given f, a function from T into S, creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else a result equivalent to:

Ordering[S].compare(f(x), f(y))

This function is equivalent to passing the result of Ordering.by(f) to orElse.

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElseBy[Int](_.b)
Source
Ordering.scala
def orElseBy[S](f: T => S)(ord: Ordering[S]): Ordering[T]

Given f, a function from T into S, creates an Ordering[T] whose compare function returns the result of this Ordering's compare function, if it is non-zero, or else a result equivalent to:

Ordering[S].compare(f(x), f(y))

This function is equivalent to passing the result of Ordering.by(f) to orElse.

Example

case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElseBy[Int](_.b)
Source
Ordering.scala
override def reverse: Ordering[T]

Return the opposite ordering of this one.

Implementations overriding this method MUST override isReverseOf as well if they change the behavior at all (for example, caching does not require overriding it).

Definition Classes
Source
Ordering.scala
def tryCompare(x: T, y: T): Option[Int]
Implicitly added by Option

Returns whether a comparison between x and y is defined, and if so the result of compare(x, y).

def tryCompare(x: T, y: T): Option[Int]
Implicitly added by Iterable

Returns whether a comparison between x and y is defined, and if so the result of compare(x, y).

def tryCompare(x: T, y: T): Option[Int]

Returns whether a comparison between x and y is defined, and if so the result of compare(x, y).

Inherited methods

def reversed(): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def reversed(): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def reversed(): Comparator[T]
Inherited from
Comparator
def thenComparing[U <: Comparable[_ >: U <: `<FromJavaObject>`]](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparing[U <: `<FromJavaObject>`](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U], `x$1`: Comparator[_ >: U <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparing(`x$0`: Comparator[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparing[U <: Comparable[_ >: U <: `<FromJavaObject>`]](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparing[U <: `<FromJavaObject>`](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U], `x$1`: Comparator[_ >: U <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparing(`x$0`: Comparator[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparing[U <: Comparable[_ >: U <: `<FromJavaObject>`]](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U]): Comparator[T]
Inherited from
Comparator
def thenComparing[U <: `<FromJavaObject>`](`x$0`: Function[_ >: T <: `<FromJavaObject>`, _ <: U], `x$1`: Comparator[_ >: U <: `<FromJavaObject>`]): Comparator[T]
Inherited from
Comparator
def thenComparing(`x$0`: Comparator[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Inherited from
Comparator
def thenComparingDouble(`x$0`: ToDoubleFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparingDouble(`x$0`: ToDoubleFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparingDouble(`x$0`: ToDoubleFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Inherited from
Comparator
def thenComparingInt(`x$0`: ToIntFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparingInt(`x$0`: ToIntFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparingInt(`x$0`: ToIntFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Inherited from
Comparator
def thenComparingLong(`x$0`: ToLongFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Option
Inherited from
Comparator
def thenComparingLong(`x$0`: ToLongFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Implicitly added by Iterable
Inherited from
Comparator
def thenComparingLong(`x$0`: ToLongFunction[_ >: T <: `<FromJavaObject>`]): Comparator[T]
Inherited from
Comparator

Implicits

Implicits

implicit def mkOrderingOps(lhs: T): OrderingOps
Implicitly added by Option

This implicit method augments T with the comparison operators defined in scala.math.Ordering.Ops.

implicit def mkOrderingOps(lhs: T): OrderingOps
Implicitly added by Iterable

This implicit method augments T with the comparison operators defined in scala.math.Ordering.Ops.

implicit def mkOrderingOps(lhs: T): OrderingOps

This implicit method augments T with the comparison operators defined in scala.math.Ordering.Ops.