Package org.apache.commons.statistics.descriptive

Class IntSumOfSquares

java.lang.Object

org.apache.commons.statistics.descriptive.IntSumOfSquares

All Implemented Interfaces:

java.util.function.DoubleSupplier, java.util.function.IntConsumer, java.util.function.IntSupplier, java.util.function.LongSupplier, IntStatistic, StatisticAccumulator<IntSumOfSquares>, StatisticResult

public final class IntSumOfSquares
extends java.lang.Object
implements IntStatistic, StatisticAccumulator<IntSumOfSquares>

Returns the sum of the squares of the available values. Uses the following definition:

\[ \sum_{i=1}^n x_i^2 \]

where \( n \) is the number of samples.

• The result is zero if no values are observed.

The implementation uses an exact integer sum to compute the sum of squared values. The exact sum is returned using getAsBigInteger(). Methods that return int or long primitives will raise an exception if the result overflows.

Note that the implementation does not use BigInteger arithmetic; for performance the sum is computed using primitives to create an unsigned 128-bit integer. Support is provided for at least 2⁶³ observations.

This class is designed to work with (though does not require) streams.

This implementation is not thread safe. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the accept or combine method, it must be synchronized externally.

However, it is safe to use accept and combine as accumulator and combiner functions of Collector 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.

Since:

1.1

Field Summary

Fields

Modifier and Type	Field	Description
private static int	SMALL_SAMPLE	Small array sample size.
private UInt128	sumSq	Sum of the squared values.

Constructor Summary

Constructors

Modifier	Constructor	Description
private	IntSumOfSquares()	Create an instance.
private	IntSumOfSquares(UInt128 sumSq)	Create an instance.

Method Summary

Modifier and Type	Method	Description
void	accept(int value)	Updates the state of the statistic to reflect the addition of value.
IntSumOfSquares	combine(IntSumOfSquares other)	Combines the state of the other statistic into this one.
static IntSumOfSquares	create()	Creates an instance.
java.math.BigInteger	getAsBigInteger()	Gets the sum of squares of all input values.
double	getAsDouble()	Gets the sum of squares of all input values.
int	getAsInt()	Gets the sum of squares of all input values.
long	getAsLong()	Gets the sum of squares of all input values.
(package private) UInt128	getSumOfSquares()	Gets the sum of squares.
static IntSumOfSquares	of(int... values)	Returns an instance populated using the input values.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.function.IntConsumer

andThen

Field Detail

SMALL_SAMPLE

private static final int SMALL_SAMPLE

Small array sample size. Used to avoid computing with UInt96 then converting to UInt128.

See Also:

Constant Field Values

sumSq

private final UInt128 sumSq

Sum of the squared values.

Constructor Detail

IntSumOfSquares

private IntSumOfSquares()

Create an instance.

IntSumOfSquares

private IntSumOfSquares(UInt128 sumSq)

Create an instance.

Parameters:

sumSq - Sum of the squared values.

Method Detail

create

public static IntSumOfSquares create()

Creates an instance.

The initial result is zero.

Returns:

IntSumOfSquares instance.

of

public static IntSumOfSquares of(int... values)

Returns an instance populated using the input values.

Parameters:

values - Values.

Returns:

IntSumOfSquares instance.

getSumOfSquares

UInt128 getSumOfSquares()

Gets the sum of squares.

This is package private for use in IntStatistics.

Returns:

the sum of squares

accept

public void accept(int value)

Updates the state of the statistic to reflect the addition of value.

Specified by:

accept in interface java.util.function.IntConsumer

Parameters:

value - Value.

getAsInt

public int getAsInt()

Gets the sum of squares of all input values.

When no values have been added, the result is zero.

Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^31).

Specified by:

getAsInt in interface java.util.function.IntSupplier

Specified by:

getAsInt in interface StatisticResult

Returns:

sum of all values.

Throws:

java.lang.ArithmeticException - if the result overflows an int

See Also:

getAsBigInteger()

getAsLong

public long getAsLong()

Gets the sum of squares of all input values.

When no values have been added, the result is zero.

Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^63).

Specified by:

getAsLong in interface java.util.function.LongSupplier

Specified by:

getAsLong in interface StatisticResult

Returns:

sum of all values.

Throws:

java.lang.ArithmeticException - if the result overflows a long

See Also:

getAsBigInteger()

getAsDouble

public double getAsDouble()

Gets the sum of squares of all input values.

When no values have been added, the result is zero.

Note that this conversion can lose information about the precision of the BigInteger value.

Specified by:

getAsDouble in interface java.util.function.DoubleSupplier

Returns:

sum of squares of all values.

See Also:

getAsBigInteger()

getAsBigInteger

public java.math.BigInteger getAsBigInteger()

Gets the sum of squares of all input values.

When no values have been added, the result is zero.

Specified by:

getAsBigInteger in interface StatisticResult

Returns:

sum of squares of all values.

combine

public IntSumOfSquares combine(IntSumOfSquares other)

Description copied from interface: StatisticAccumulator

Combines the state of the other statistic into this one.

Specified by:

combine in interface StatisticAccumulator<IntSumOfSquares>

Parameters:

other - Another statistic to be combined.

Returns:

this instance after combining other.