com.clearspring.analytics.stream.cardinality

Class LinearCounting

java.lang.Object

com.clearspring.analytics.stream.cardinality.LinearCounting

All Implemented Interfaces:

ICardinality

public class LinearCounting
extends Object
implements ICardinality

See A Linear-Time Probabilistic Counting Algorithm for Database Applications by Whang, Vander-Zanden, Taylor

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	LinearCounting.Builder
protected static class	LinearCounting.LinearCountingMergeException

Field Summary

Fields

Modifier and Type	Field and Description
protected int	count Number of bits left unset in the map
protected int	length Size of the map in bits
protected byte[]	map Bitmap Hashed stream elements are mapped to bits in this array

Constructor Summary

Constructors

Constructor and Description
LinearCounting(byte[] map)
LinearCounting(int size)

Method Summary

Methods

Modifier and Type	Method and Description
long	cardinality()
protected int	computeCount()
byte[]	getBytes()
int	getCount()
double	getUtilization()
boolean	isSaturated()
protected String	mapAsBitString() For debug purposes
ICardinality	merge(ICardinality... estimators) Merges estimators to produce a new estimator for the combined streams of this estimator and those passed as arguments.
static LinearCounting	mergeEstimators(LinearCounting... estimators) Merges estimators to produce an estimator for their combined streams
boolean	offer(Object o)
boolean	offerHashed(int hashedInt) Offer the value as a hashed long value
boolean	offerHashed(long hashedLong) Offer the value as a hashed long value
int	sizeof()

Methods inherited from class java.lang.Object

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

Field Detail

map

protected byte[] map

Bitmap Hashed stream elements are mapped to bits in this array

length

protected final int length

Size of the map in bits

count

protected int count

Number of bits left unset in the map

Constructor Detail

LinearCounting

public LinearCounting(int size)

Parameters:

size - of bit array in bytes

LinearCounting

public LinearCounting(byte[] map)

Method Detail

cardinality

public long cardinality()

Specified by:

cardinality in interface ICardinality

Returns:

the number of unique elements in the stream or an estimate thereof

getBytes

public byte[] getBytes()

Specified by:

getBytes in interface ICardinality

Returns:

offerHashed

public boolean offerHashed(long hashedLong)

Description copied from interface: ICardinality

Offer the value as a hashed long value

Specified by:

offerHashed in interface ICardinality

Parameters:

hashedLong - - the hash of the item to offer to the estimator

Returns:

false if the value returned by cardinality() is unaffected by the appearance of hashedLong in the stream

offerHashed

public boolean offerHashed(int hashedInt)

Description copied from interface: ICardinality

Offer the value as a hashed long value

Specified by:

offerHashed in interface ICardinality

Parameters:

hashedInt - - the hash of the item to offer to the estimator

Returns:

false if the value returned by cardinality() is unaffected by the appearance of hashedInt in the stream

offer

public boolean offer(Object o)

Specified by:

offer in interface ICardinality

Parameters:

o - stream element

Returns:

false if the value returned by cardinality() is unaffected by the appearance of o in the stream.

sizeof

public int sizeof()

Specified by:

sizeof in interface ICardinality

Returns:

size in bytes needed for serialization

computeCount

protected int computeCount()

getUtilization

public double getUtilization()

Returns:

(# set bits) / (total # of bits)

getCount

public int getCount()

isSaturated

public boolean isSaturated()

mapAsBitString

protected String mapAsBitString()

For debug purposes

Returns:

merge

public ICardinality merge(ICardinality... estimators)
                   throws LinearCounting.LinearCountingMergeException

Description copied from interface: ICardinality

Merges estimators to produce a new estimator for the combined streams of this estimator and those passed as arguments. Nor this estimator nor the one passed as parameters are modified.

Specified by:

merge in interface ICardinality

Parameters:

estimators - Zero or more compatible estimators

Returns:

this if estimators is null or no arguments are passed

Throws:

LinearCounting.LinearCountingMergeException - if estimators are not mergeable (all estimators must be instances of LinearCounting of the same size)

mergeEstimators

public static LinearCounting mergeEstimators(LinearCounting... estimators)
                                      throws LinearCounting.LinearCountingMergeException

Merges estimators to produce an estimator for their combined streams

Parameters:

estimators -

Returns:

merged estimator or null if no estimators were provided

Throws:

LinearCounting.LinearCountingMergeException - if estimators are not mergeable (all estimators must be the same size)