Ordering

Companion object Ordering

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.

Self Type: Ordering[T]
Annotations: @implicitNotFound(msg = "No implicit Ordering defined for ${T}.")
Source: Ordering.scala
See also: scala.math.Ordered, scala.util.Sorting

Linear Supertypes

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

Known Subclasses

ValueOrdering, DeadlineIsOrdered, DurationIsOrdered, FiniteDurationIsOrdered, Fractional, Integral, Numeric, BigDecimalAsIfIntegral, BigDecimalAsIfIntegral, BigDecimalIsConflicted, BigDecimalIsFractional, BigDecimalIsFractional, BigIntIsIntegral, BigIntIsIntegral, ByteIsIntegral, ByteIsIntegral, CharIsIntegral, CharIsIntegral, DoubleIsFractional, DoubleIsFractional, FloatIsFractional, FloatIsFractional, IntIsIntegral, IntIsIntegral, LongIsIntegral, LongIsIntegral, ShortIsIntegral, ShortIsIntegral, BigDecimal, BigDecimalOrdering, BigInt, BigIntOrdering, Boolean, BooleanOrdering, Byte, ByteOrdering, CachedReverse, Char, CharOrdering, DeprecatedDoubleOrdering, DeprecatedFloatOrdering, IeeeOrdering, IeeeOrdering, TotalOrdering, TotalOrdering, IeeeOrdering, IeeeOrdering, TotalOrdering, TotalOrdering, Int, IntOrdering, Long, LongOrdering, OptionOrdering, Short, ShortOrdering, String, StringOrdering, Symbol, SymbolOrdering, Unit, UnitOrdering

Type Hierarchy

Ordering

Alphabetic
By Inheritance

Inherited

Ordering
PartialOrdering
Equiv
Serializable
Comparator
AnyRef
Any

Implicitly

by any2stringadd
by StringFormat
by Ensuring
by ArrowAssoc

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Visibility

Public
Protected

Type Members

class OrderingOps 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
Test two objects for inequality.
Test two objects for inequality.
returns
true if !(this == that), false otherwise.
Definition Classes
AnyRef → Any
final def ##: Int
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.
returns
a hash value consistent with ==
Definition Classes
AnyRef → Any
def +(other: String): String
Implicit
This member is added by an implicit conversion from Ordering[T] toany2stringadd[Ordering[T]] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd
def ->[B](y: B): (Ordering[T], B)
Implicit
This member is added by an implicit conversion from Ordering[T] toArrowAssoc[Ordering[T]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
returns
true if the receiver object is equivalent to the argument; false otherwise.
Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0
Cast the receiver object to be of type T0.
Cast the receiver object to be of type T0.
Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.
returns
the receiver object.
Definition Classes
Any
Exceptions thrown
ClassCastException if the receiver object is not an instance of the erasure of type T0.
def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the clone method is platform dependent.
returns
a copy of the receiver object.
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note
not specified by SLS as a member of AnyRef
def ensuring(cond: (Ordering[T]) => Boolean, msg: => Any): Ordering[T]
Implicit
This member is added by an implicit conversion from Ordering[T] toEnsuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: (Ordering[T]) => Boolean): Ordering[T]
Implicit
This member is added by an implicit conversion from Ordering[T] toEnsuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean, msg: => Any): Ordering[T]
Implicit
This member is added by an implicit conversion from Ordering[T] toEnsuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
def ensuring(cond: Boolean): Ordering[T]
Implicit
This member is added by an implicit conversion from Ordering[T] toEnsuring[Ordering[T]] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
Tests whether the argument (that) is a reference to the receiver object (this).
The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:
- It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
- For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
- null.eq(null) returns true.
When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).
returns
true if the argument is a reference to the receiver object; false otherwise.
Definition Classes
AnyRef
def equals(arg0: AnyRef): Boolean
The equality method for reference types.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
returns
true if the receiver object is equivalent to the argument; false otherwise.
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
Called by the garbage collector on the receiver object when there are no more references to the object.
Called by the garbage collector on the receiver object when there are no more references to the object.
The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.
Attributes
protected[lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note
not specified by SLS as a member of AnyRef
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
This member is added by an implicit conversion from Ordering[T] toStringFormat[Ordering[T]] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()
final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
returns
a class object corresponding to the runtime type of the receiver.
Definition Classes
AnyRef → Any
Annotations
@native()
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
The hashCode method for reference types.
The hashCode method for reference types. See hashCode in scala.Any.
returns
the hash code value for this object.
Definition Classes
AnyRef → Any
Annotations
@native()
final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object is T0.
Test whether the dynamic type of the receiver object is T0.
Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.
returns
true if the receiver object is an instance of erasure of type T0; false otherwise.
Definition Classes
Any
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.
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[U <: T](x: U, y: U): U
Return x if x >= y, otherwise y.
def min[U <: T](x: U, y: U): U
Return x if x <= y, otherwise y.
implicit def mkOrderingOps(lhs: T): OrderingOps
This implicit method augments T with the comparison operators defined in scala.math.Ordering.Ops.
final def ne(arg0: AnyRef): Boolean
Equivalent to !(this eq that).
Equivalent to !(this eq that).
returns
true if the argument is not a reference to the receiver object; false otherwise.
Definition Classes
AnyRef
final def notify(): Unit
Wakes up a single thread that is waiting on the receiver object's monitor.
Wakes up a single thread that is waiting on the receiver object's monitor.
Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
final def notifyAll(): Unit
Wakes up all threads that are waiting on the receiver object's monitor.
Wakes up all threads that are waiting on the receiver object's monitor.
Definition Classes
AnyRef
Annotations
@native()
Note
not specified by SLS as a member of 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 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.
other
an Ordering to use if this Ordering returns zero
Example:
1. case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElse(Ordering.by[Pair, Int](_.b))
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:
1. case class Pair(a: Int, b: Int) val pairOrdering = Ordering.by[Pair, Int](_.a) .orElseBy[Int](_.b)
def reverse: Ordering[T]
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
Ordering → PartialOrdering
def reversed(): Comparator[T]
Definition Classes
Comparator
final def synchronized[T0](arg0: => T0): T0
Definition Classes
AnyRef
def thenComparing[U <: Comparable[_ >: U <: AnyRef]](arg0: java.util.function.Function[_ >: T <: AnyRef, _ <: U]): Comparator[T]
Definition Classes
Comparator
def thenComparing[U <: AnyRef](arg0: java.util.function.Function[_ >: T <: AnyRef, _ <: U], arg1: Comparator[_ >: U <: AnyRef]): Comparator[T]
Definition Classes
Comparator
def thenComparing(arg0: Comparator[_ >: T <: AnyRef]): Comparator[T]
Definition Classes
Comparator
def thenComparingDouble(arg0: ToDoubleFunction[_ >: T <: AnyRef]): Comparator[T]
Definition Classes
Comparator
def thenComparingInt(arg0: ToIntFunction[_ >: T <: AnyRef]): Comparator[T]
Definition Classes
Comparator
def thenComparingLong(arg0: ToLongFunction[_ >: T <: AnyRef]): Comparator[T]
Definition Classes
Comparator
def toString(): String
Creates a String representation of this object.
Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.
returns
a String representation of the object.
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(classOf[java.lang.InterruptedException])
final def wait(arg0: Long, arg1: Int): Unit
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
final def wait(arg0: Long): Unit
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

Deprecated Value Members

def →[B](y: B): (Ordering[T], B)
Implicit
This member is added by an implicit conversion from Ordering[T] toArrowAssoc[Ordering[T]] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@deprecated
Deprecated
(Since version 2.13.0) Use -> instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.

Packages

Package structure

Automatic imports

Ordering

Companion object Ordering

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

Type Members

Abstract Value Members

Concrete Value Members

Deprecated Value Members

Inherited from PartialOrdering[T]

Inherited from Equiv[T]

Inherited from java.io.Serializable

Inherited from Comparator[T]

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromOrdering[T] to any2stringadd[Ordering[T]]

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

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

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

Ungrouped

Packages

Package structure

Automatic imports

Ordering

Companion object Ordering

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

Type Members

Abstract Value Members

Concrete Value Members

Deprecated Value Members

Inherited from PartialOrdering[T]

Inherited from Equiv[T]

Inherited from java.io.Serializable

Inherited from Comparator[T]

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd fromOrdering[T] to any2stringadd[Ordering[T]]

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

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

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

Ungrouped

Ordering