Ordering

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.

Self Type: Ordering[T]
Annotations: @implicitNotFound( msg = ... )
Version: 0.9.5, 2008-04-15
Since: 2.7
See also: scala.math.Ordered, scala.util.Sorting

Linear Supertypes

PartialOrdering[T], Equiv[T], Serializable, java.io.Serializable, Comparator[T], AnyRef, Any

Known Subclasses

BigDecimal, BigDecimalAsIfIntegral, BigDecimalAsIfIntegral, BigDecimalIsConflicted, BigDecimalIsFractional, BigDecimalIsFractional, BigDecimalOrdering, BigInt, BigIntIsIntegral, BigIntIsIntegral, BigIntOrdering, Boolean, BooleanOrdering, Byte, ByteIsIntegral, ByteIsIntegral, ByteOrdering, Char, CharIsIntegral, CharIsIntegral, CharOrdering, DeadlineIsOrdered, Double, DoubleAsIfIntegral, DoubleAsIfIntegral, DoubleIsConflicted, DoubleIsFractional, DoubleIsFractional, DoubleOrdering, DurationIsOrdered, FiniteDurationIsOrdered, Float, FloatAsIfIntegral, FloatAsIfIntegral, FloatIsConflicted, FloatIsFractional, FloatIsFractional, FloatOrdering, Fractional, Int, IntIsIntegral, IntIsIntegral, IntOrdering, Integral, Long, LongIsIntegral, LongIsIntegral, LongOrdering, Numeric, OptionOrdering, Short, ShortIsIntegral, ShortIsIntegral, ShortOrdering, String, StringOrdering, Unit, UnitOrdering, ValueOrdering

Type Members

class Ops extends AnyRef

This inner class defines comparison operators available for T.

Abstract Value Members

abstract 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)
Definition Classes
Ordering → Comparator

Concrete Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
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
Ordering → PartialOrdering → Equiv
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
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
Ordering → PartialOrdering
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
Ordering → PartialOrdering
def hashCode(): Int

Definition Classes
AnyRef → Any
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
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
Ordering → PartialOrdering
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
Ordering → PartialOrdering
def max(x: T, y: T): T

Return x if x >= y, otherwise y.
def min(x: T, y: T): T

Return x if x <= y, otherwise y.
implicit def mkOrderingOps(lhs: T): Ops

This implicit method augments T with the comparison operators defined in scala.math.Ordering.Ops.
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
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))
```
def reverse: Ordering[T]

Return the opposite ordering of this one.
Return the opposite ordering of this one.

Definition Classes
Ordering → PartialOrdering
def reversed(): Comparator[T]

Definition Classes
Comparator
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def thenComparing[U <: Comparable[_ >: U]](arg0: java.util.function.Function[_ >: T, _ <: U]): Comparator[T]

Definition Classes
Comparator
def thenComparing[U](arg0: java.util.function.Function[_ >: T, _ <: U], arg1: Comparator[_ >: U]): Comparator[T]

Definition Classes
Comparator
def thenComparing(arg0: Comparator[_ >: T]): Comparator[T]

Definition Classes
Comparator
def thenComparingDouble(arg0: ToDoubleFunction[_ >: T]): Comparator[T]

Definition Classes
Comparator
def thenComparingInt(arg0: ToIntFunction[_ >: T]): Comparator[T]

Definition Classes
Comparator
def thenComparingLong(arg0: ToLongFunction[_ >: T]): Comparator[T]

Definition Classes
Comparator
def toString(): String

Definition Classes
AnyRef → Any
def tryCompare(x: T, y: T): Some[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).

Definition Classes
Ordering → PartialOrdering
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Docs: object Ordering | package math

trait Ordering[T] extends Comparator[T] with PartialOrdering[T] with Serializable

Type Members

class Ops extends AnyRef

Abstract Value Members

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

Concrete Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

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

def finalize(): Unit

final def getClass(): Class[_]

def gt(x: T, y: T): Boolean

def gteq(x: T, y: T): Boolean

def hashCode(): Int

final def isInstanceOf[T0]: Boolean

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

def lteq(x: T, y: T): Boolean

def max(x: T, y: T): T

def min(x: T, y: T): T

implicit def mkOrderingOps(lhs: T): Ops

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

def on[U](f: (U) ⇒ T): Ordering[U]

def reverse: Ordering[T]

def reversed(): Comparator[T]

final def synchronized[T0](arg0: ⇒ T0): T0

def thenComparing[U <: Comparable[_ >: U]](arg0: java.util.function.Function[_ >: T, _ <: U]): Comparator[T]

def thenComparing[U](arg0: java.util.function.Function[_ >: T, _ <: U], arg1: Comparator[_ >: U]): Comparator[T]

def thenComparing(arg0: Comparator[_ >: T]): Comparator[T]

def thenComparingDouble(arg0: ToDoubleFunction[_ >: T]): Comparator[T]

def thenComparingInt(arg0: ToIntFunction[_ >: T]): Comparator[T]

def thenComparingLong(arg0: ToLongFunction[_ >: T]): Comparator[T]

def toString(): String

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

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from PartialOrdering[T]

Inherited from Equiv[T]

Inherited from Serializable

Inherited from java.io.Serializable

Inherited from Comparator[T]

Inherited from AnyRef

Inherited from Any

Ungrouped