Module io.jenetics.base

Package io.jenetics.stat

Class Quantile

java.lang.Object

io.jenetics.stat.Quantile

All Implemented Interfaces:

DoubleConsumer

public class Quantile
extends Object
implements DoubleConsumer

Implementation of the quantile estimation algorithm published by

Raj JAIN and Imrich CHLAMTAC: The P² Algorithm for Dynamic Calculation of Quantiles and Histograms Without Storing Observations
[Communications of the ACM; October 1985, Volume 28, Number 10]

This class is designed to work with (though does not require) streams. For example, you can compute the quantile with:

final DoubleStream stream = ...;
final Quantile quantile = stream.collect(
        () -> new Quantile(0.23),
        Quantile::accept,
        Quantile::combine
    );

Since:

1.0

Version:

6.0

See Also:

• Wikipedia: Quantile

Implementation Note:

This implementation is not thread safe. However, it is safe to use on a parallel stream, because the parallel implementation of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution. Using this class in the collect method of a parallel stream can lead to a reduced accuracy of the quantile value. Since this implementation is an estimation algorithm, combining the estimations will only work for large streams (size >> 1000).

Constructor Summary

Constructors

Constructor	Description
Quantile(double quantile)	Create a new quantile accumulator with the given value.

Method Summary

Modifier and Type	Method	Description
void	accept(double value)
Quantile	combine(Quantile other)	Combine two Quantile objects.
long	count()	Return the number of samples the quantile value was calculated of.
double	quantile()	Return the quantile this object has been parametrized with.
void	reset()	Reset this object to its initial state.
boolean	sameState(Quantile other)	Compares the state of two Quantile objects.
static <T> Collector<T,?,Quantile>	toMedian(ToDoubleFunction<? super T> mapper)	Return a Collector which applies a double-producing mapping function to each input element, and returns the median for the resulting values.
static <T> Collector<T,?,Quantile>	toQuantile(double quantile, ToDoubleFunction<? super T> mapper)	Return a Collector which applies a double-producing mapping function to each input element, and returns quantiles for the resulting values.
String	toString()
double	value()	Return the computed quantile value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.function.DoubleConsumer

andThen

Constructor Details

Quantile

public Quantile(double quantile)

Create a new quantile accumulator with the given value.

Parameters:

quantile - the wished quantile value.

Throws:

IllegalArgumentException - if the quantile is not in the range [0, 1].

Method Details

reset

public void reset()

Reset this object to its initial state.

quantile

public double quantile()

Return the quantile this object has been parametrized with.

Returns:

the quantile this object has been parametrized with

Since:

3.1

value

public double value()

Return the computed quantile value.

Returns:

the quantile value.

count

public long count()

Return the number of samples the quantile value was calculated of.

Returns:

the number of samples the quantile value was calculated of

accept

public void accept(double value)

Specified by:

accept in interface DoubleConsumer

combine

public Quantile combine(Quantile other)

Combine two Quantile objects.

Parameters:

other - the other Quantile object to combine

Returns:

this

Throws:

NullPointerException - if the other object is null.

IllegalArgumentException - if the quantile() of the other object differs from this one.

Since:

3.1

sameState

public boolean sameState(Quantile other)

Compares the state of two Quantile objects. This is a replacement for the Object.equals(Object) which is not advisable to implement for this mutable object. If two objects have the same state, it has still the same state when updated with the same value.

final Quantile q1 = ...;
final Quantile q2 = ...;

if (q1.sameState(q2)) {
    final double value = random.nextDouble();
    q1.accept(value);
    q2.accept(value);

    assert q1.sameState(q2);
    assert q2.sameState(q1);
    assert q1.sameState(q1);
}

Parameters:

other - the other object for the test

Returns:

true the this and the other objects have the same state, false otherwise

Since:

3.7

toString

public String toString()

Overrides:

toString in class Object

toQuantile

public static <T> Collector<T,?,Quantile> toQuantile(double quantile,
 ToDoubleFunction<? super T> mapper)

Return a Collector which applies a double-producing mapping function to each input element, and returns quantiles for the resulting values.

final Stream<SomeObject> stream = ...;
final Quantile quantile = stream
    .collect(toQuantile(0.25, v -> v.doubleValue()));

Type Parameters:

T - the type of the input elements

Parameters:

quantile - the wished quantile value.

mapper - a mapping function to apply to each element

Returns:

a Collector implementing the quantile reduction

Throws:

NullPointerException - if the given mapper is null

IllegalArgumentException - if the quantile is not in the range [0, 1].

toMedian

public static <T> Collector<T,?,Quantile> toMedian(ToDoubleFunction<? super T> mapper)

Return a Collector which applies a double-producing mapping function to each input element, and returns the median for the resulting values.

final Stream<SomeObject> stream = ...;
final Quantile median = stream.collect(toMedian(v -> v.doubleValue()));

Type Parameters:

T - the type of the input elements

Parameters:

mapper - a mapping function to apply to each element

Returns:

a Collector implementing the quantile reduction

Throws:

NullPointerException - if the given mapper is null