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 = ... )
Source: Ordering.scala
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 Hierarchy Learn more about scaladoc diagrams

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: AnyRef): Boolean

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

Definition Classes
Any
final def ##(): Int

Definition Classes
AnyRef → Any
def +(other: String): String

Implicit information
This member is added by an implicit conversion from Ordering[T] to StringAdd[Ordering[T]] performed by method StringAdd in scala.Predef.
Definition Classes
StringAdd
def ->[B](y: B): (Ordering[T], B)

Implicit information
This member is added by an implicit conversion from Ordering[T] to ArrowAssoc[Ordering[T]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()
final def ==(arg0: AnyRef): Boolean

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

Definition Classes
Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
def ensuring(cond: (Ordering[T]) ⇒ Boolean, msg: ⇒ Any): Ordering[T]

Implicit information
This member is added by an implicit conversion from Ordering[T] to Ensuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (Ordering[T]) ⇒ Boolean): Ordering[T]

Implicit information
This member is added by an implicit conversion from Ordering[T] to Ensuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: ⇒ Any): Ordering[T]

Implicit information
This member is added by an implicit conversion from Ordering[T] to Ensuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): Ordering[T]

Implicit information
This member is added by an implicit conversion from Ordering[T] to Ensuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
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] )
def formatted(fmtstr: String): String

Returns string formatted according to given format string.
Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit information
This member is added by an implicit conversion from Ordering[T] to StringFormat[Ordering[T]] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()
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
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
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( ... )
def →[B](y: B): (Ordering[T], B)

Implicit information
This member is added by an implicit conversion from Ordering[T] to ArrowAssoc[Ordering[T]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc

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: AnyRef): Boolean

final def !=(arg0: Any): Boolean

final def ##(): Int

def +(other: String): String

def ->[B](y: B): (Ordering[T], B)

final def ==(arg0: AnyRef): Boolean

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

def ensuring(cond: (Ordering[T]) ⇒ Boolean, msg: ⇒ Any): Ordering[T]

def ensuring(cond: (Ordering[T]) ⇒ Boolean): Ordering[T]

def ensuring(cond: Boolean, msg: ⇒ Any): Ordering[T]

def ensuring(cond: Boolean): Ordering[T]

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

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

def finalize(): Unit

def formatted(fmtstr: String): String

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]

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

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

def →[B](y: B): (Ordering[T], B)

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

Inherited by implicit conversion StringAdd from Ordering[T] to StringAdd[Ordering[T]]

Inherited by implicit conversion StringFormat from Ordering[T] to StringFormat[Ordering[T]]

Inherited by implicit conversion Ensuring from Ordering[T] to Ensuring[Ordering[T]]

Inherited by implicit conversion ArrowAssoc from Ordering[T] to ArrowAssoc[Ordering[T]]

Ungrouped