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.

See also
Companion
object
Source
Ordering.scala
trait Equiv[T]
trait Comparator[T]
class Object
trait Matchable
class Any

Type members

Classlikes

class OrderingOps(lhs: T)
Implicitly added by Iterable

This inner class defines comparison operators available for 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.

Source
Ordering.scala
class OrderingOps(lhs: T)
Implicitly added by Option

This inner class defines comparison operators available for 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.

Source
Ordering.scala
class OrderingOps(lhs: T)

This inner class defines comparison operators available for 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.

Source
Ordering.scala

Value members

Abstract methods

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

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

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)

Source
Ordering.scala
def compare(x: T, y: T): Int
Implicitly added by Option

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

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)

Source
Ordering.scala
def compare(x: T, y: T): Int

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

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)

Source
Ordering.scala

Concrete methods

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

Return true if x == y in the ordering.

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.

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.

Return true if x >= y in the ordering.

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

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

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.

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.

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.

Source
Ordering.scala
def isReverseOf(other: Ordering[_]): Boolean

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

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.

Source
Ordering.scala
override
def lt(x: T, y: T): Boolean

Return true if x < y in the ordering.

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.

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 Iterable

Return x if x >= y, otherwise y.

Return x if x >= y, otherwise y.

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

Return x if x >= y, otherwise y.

Return x if x >= y, otherwise y.

Source
Ordering.scala
def max[U <: T](x: U, y: U): U

Return x if x >= y, otherwise y.

Return x if x >= y, otherwise y.

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

Return x if x <= y, otherwise y.

Return x if x <= y, otherwise y.

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

Return x if x <= y, otherwise y.

Return x if x <= y, otherwise y.

Source
Ordering.scala
def min[U <: T](x: U, y: U): U

Return x if x <= y, otherwise y.

Return x if x <= y, otherwise y.

Source
Ordering.scala
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:

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))
Source
Ordering.scala
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:

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))
Source
Ordering.scala
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:

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))
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.

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 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.

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.

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)(implicit 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:

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)(implicit 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:

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)(implicit 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:

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

Return the opposite ordering of this one.

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 Iterable

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

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

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).

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

Source
Ordering.scala
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).

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

Source
Ordering.scala

Inherited methods

Implicitly added by Iterable
Inherited from
Comparator
Implicitly added by Option
Inherited from
Comparator
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]
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]
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 Iterable
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]
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]
Implicitly added by Option
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 Iterable
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]
Inherited from
Comparator

Implicits

Implicits

implicit
Implicitly added by Iterable

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

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

Source
Ordering.scala
implicit
Implicitly added by Option

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

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

Source
Ordering.scala
implicit

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

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

Source
Ordering.scala