com.yahoo.sketches.sampling

Class ReservoirLongsSketch

java.lang.Object

com.yahoo.sketches.sampling.ReservoirLongsSketch

public final class ReservoirLongsSketch
extends Object

This sketch provides a reservoir sample over an input stream of longs. The sketch contains a uniform random sample of items from the stream.

Author:

Jon Malkin, Kevin Lang

Method Summary

Modifier and Type	Method and Description
static ReservoirLongsSketch	getInstance(int k) Construct a mergeable reservoir sampling sketch with up to k samples using the default resize factor (8).
static ReservoirLongsSketch	getInstance(int k, ResizeFactor rf) Construct a mergeable reservoir sampling sketch with up to k samples using the default resize factor (8).
static ReservoirLongsSketch	getInstance(Memory srcMem) Returns a sketch instance of this class from the given srcMem, which must be a Memory representation of this sketch class.
int	getK() Returns the sketch's value of k, the maximum number of samples stored in the reservoir.
long	getN() Returns the number of items processed from the input stream
int	getNumSamples() Returns the current number of items in the reservoir, which may be smaller than the reservoir capacity.
long[]	getSamples() Returns a copy of the items in the reservoir.
byte[]	toByteArray() Returns a byte array representation of this sketch
String	toString() Returns a human-readable summary of the sketch, without data.
void	update(long item) Randomly decide whether or not to include an item in the sample set.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static ReservoirLongsSketch getInstance(int k)

Construct a mergeable reservoir sampling sketch with up to k samples using the default resize factor (8).

Parameters:

k - Maximum size of sampling. Allocated size may be smaller until sampling fills. Unlike many sketches in this package, this value does not need to be a power of 2.

Returns:

A ReservoirLongsSketch initialized with maximum size k and the default resize factor.

getInstance

public static ReservoirLongsSketch getInstance(int k,
                                               ResizeFactor rf)

Construct a mergeable reservoir sampling sketch with up to k samples using the default resize factor (8).

Parameters:

k - Maximum size of sampling. Allocated size may be smaller until sampling fills. Unlike many sketches in this package, this value does not need to be a power of 2.

rf - See Resize Factor

Returns:

A ReservoirLongsSketch initialized with maximum size k and ResizeFactor rf.

getInstance

public static ReservoirLongsSketch getInstance(Memory srcMem)

Returns a sketch instance of this class from the given srcMem, which must be a Memory representation of this sketch class.

Parameters:

srcMem - a Memory representation of a sketch of this class. See Memory

Returns:

a sketch instance of this class

getK

public int getK()

Returns the sketch's value of k, the maximum number of samples stored in the reservoir. The current number of items in the sketch may be lower.

Returns:

k, the maximum number of samples in the reservoir

getN

public long getN()

Returns the number of items processed from the input stream

Returns:

n, the number of stream items the sketch has seen

getNumSamples

public int getNumSamples()

Returns the current number of items in the reservoir, which may be smaller than the reservoir capacity.

Returns:

the number of items currently in the reservoir

getSamples

public long[] getSamples()

Returns a copy of the items in the reservoir. The returned array length may be smaller than the reservoir capacity.

Returns:

A copy of the reservoir array

update

public void update(long item)

Randomly decide whether or not to include an item in the sample set.

Parameters:

item - a unit-weight (equivalently, unweighted) item of the set being sampled from

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 sketch

Returns:

a byte array representation of this sketch