com.yahoo.sketches.sampling

Class ReservoirLongsUnion

java.lang.Object

com.yahoo.sketches.sampling.ReservoirLongsUnion

public final class ReservoirLongsUnion
extends Object

Class to union reservoir samples of longs.

For efficiency reasons, the unioning process picks one of the two sketches to use as the base. As a result, we provide only a stateful union. Using the same approach for a merge would result in unpredictable side effects on the underlying sketches.

A union object is created with a maximum value of k, represented using the ReservoirSize class. The unioning process may cause the actual number of samples to fall below that maximum value, but never to exceed it. The result of a union will be a reservoir where each item from the global input has a uniform probability of selection, but there are no claims about higher order statistics. For instance, in general all possible permutations of the global input are not equally likely.

Author:

Jon Malkin, Kevin Lang

Method Summary

Modifier and Type	Method and Description
static ReservoirLongsUnion	getInstance(int maxK) Creates an empty Union with a maximum reservoir capacity of size k, subject to the precision of ReservoirSize
static ReservoirLongsUnion	getInstance(Memory srcMem) Instantiates a Union from Memory
int	getMaxK() Returns the maximum allowed reservoir capacity in this union.
ReservoirLongsSketch	getResult() Returns a sketch representing the current state of the union.
byte[]	toByteArray() Returns a byte array representation of this union
String	toString() Returns a human-readable summary of the sketch, without data.
void	update(long datum) Present this union with a long.
void	update(Memory mem) Union the given Memory image of the sketch.
void	update(ReservoirLongsSketch sketchIn) Union the given sketch.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static ReservoirLongsUnion getInstance(int maxK)

Creates an empty Union with a maximum reservoir capacity of size k, subject to the precision of ReservoirSize

Parameters:

maxK - The maximum allowed reservoir capacity for any sketches in the union

Returns:

A new ReservoirLongsUnion

getInstance

public static ReservoirLongsUnion getInstance(Memory srcMem)

Instantiates a Union from Memory

Parameters:

srcMem - Memory object containing a serialized union

Returns:

A ReservoirLongsUnion created from the provided Memory

getMaxK

public int getMaxK()

Returns the maximum allowed reservoir capacity in this union. The current reservoir capacity may be lower.

Returns:

The maximum allowed reservoir capacity in this union.

update

public void update(ReservoirLongsSketch sketchIn)

Union the given sketch.

This method can be repeatedly called. If the given sketch is null it is interpreted as an empty sketch.

Parameters:

sketchIn - The incoming sketch.

update

public void update(Memory mem)

Union the given Memory image of the sketch.

This method can be repeatedly called. If the given sketch is null it is interpreted as an empty sketch.

Parameters:

mem - Memory image of sketch to be merged

update

public void update(long datum)

Present this union with a long.

Parameters:

datum - The given long datum.

getResult

public ReservoirLongsSketch getResult()

Returns a sketch representing the current state of the union.

Returns:

The result of any unions already processed.

toString

public String toString()

Returns a human-readable summary of the sketch, without data.

Overrides:

toString in class Object

Returns:

A string version of the sketch summary

toByteArray

public byte[] toByteArray()

Returns a byte array representation of this union

Returns:

a byte array representation of this union