An implementation of an Exact and Bounded Sampling Proportional to Size sketch. More...

#include <ebpps_sketch.hpp>

Public Member Functions
	ebpps_sketch (uint32_t k, const A &allocator=A())
	Constructor.

void	update (const T &item, double weight=1.0)
	Updates this sketch with the given data item with the given weight.

void	update (T &&item, double weight=1.0)
	Updates this sketch with the given data item with the given weight.

void	merge (const ebpps_sketch< T, A > &sketch)
	Merges the provided sketch into the current one.

void	merge (ebpps_sketch< T, A > &&sketch)
	Merges the provided sketch into the current one.

result_type	get_result () const
	Returns a copy of the current sample, as a std::vector.

uint32_t	get_k () const
	Returns the configured maximum sample size.

uint64_t	get_n () const
	Returns the number of items processed by the sketch, regardless of item weight.

double	get_cumulative_weight () const
	Returns the cumulative weight of items processed by the sketch.

double	get_c () const
	Returns the expected number of samples returned upon a call to get_result() or the creation of an iterator.

bool	is_empty () const
	Returns true if the sketch is empty.

A	get_allocator () const
	Returns an instance of the allocator for this sketch.

void	reset ()
	Resets the sketch to its default, empty state.

template<typename SerDe = serde<T>>
size_t	get_serialized_size_bytes (const SerDe &sd=SerDe()) const
	Computes size needed to serialize the current state of the sketch.

template<typename SerDe = serde<T>>
vector_bytes	serialize (unsigned header_size_bytes=0, const SerDe &sd=SerDe()) const
	This method serializes the sketch as a vector of bytes.

template<typename SerDe = serde<T>>
void	serialize (std::ostream &os, const SerDe &sd=SerDe()) const
	This method serializes the sketch into a given stream in a binary form.

string< A >	to_string () const
	Prints a summary of the sketch.

string< A >	items_to_string () const
	Prints the raw sketch items to a string.

ebpps_sample< T, A >::const_iterator	begin () const
	Iterator pointing to the first item in the sketch.

ebpps_sample< T, A >::const_iterator	end () const
	Iterator pointing to the past-the-end item in the sketch.

Static Public Member Functions
template<typename SerDe = serde<T>>
static ebpps_sketch	deserialize (const void *bytes, size_t size, const SerDe &sd=SerDe(), const A &allocator=A())
	This method deserializes a sketch from a given array of bytes.

template<typename SerDe = serde<T>>
static ebpps_sketch	deserialize (std::istream &is, const SerDe &sd=SerDe(), const A &allocator=A())
	This method deserializes a sketch from a given stream.

Detailed Description

template<typename T, typename A = std::allocator<T>>
class datasketches::ebpps_sketch< T, A >

An implementation of an Exact and Bounded Sampling Proportional to Size sketch.

From: "Exact PPS Sampling with Bounded Sample Size", B. Hentschel, P. J. Haas, Y. Tian. Information Processing Letters, 2023.

This sketch samples data from a stream of items proportional to the weight of each item. The sample guarantees the presence of an item in the result is proportional to that item's portion of the total weight seen by the sketch, and returns a sample no larger than size k.

The sample may be smaller than k and the resulting size of the sample potentially includes a probabilistic component, meaning the resulting sample size is not always constant.

Author: Jon Malkin

Constructor & Destructor Documentation

◆ ebpps_sketch()

template<typename T , typename A >

ebpps_sketch	(	uint32_t	k,
		const A &	allocator = `A()`
	)

explicit

Constructor.

Parameters

k	sketch size
allocator	instance of an allocator

Member Function Documentation

◆ update() [1/2]

template<typename T , typename A >

void update	(	const T &	item,
		double	weight = `1.0`
	)

Updates this sketch with the given data item with the given weight.

This method takes an lvalue.

Parameters

item	an item from a stream of items
weight	the weight of the item

◆ update() [2/2]

template<typename T , typename A >

void update	(	T &&	item,
		double	weight = `1.0`
	)

Updates this sketch with the given data item with the given weight.

This method takes an rvalue.

Parameters

item	an item from a stream of items
weight	the weight of the item

◆ merge() [1/2]

template<typename T , typename A >

void merge ( const ebpps_sketch< T, A > & sketch )

Merges the provided sketch into the current one.

This method takes an lvalue.

Parameters

sketch the sketch to merge into the current object

◆ merge() [2/2]

template<typename T , typename A >

void merge ( ebpps_sketch< T, A > && sketch )

Merges the provided sketch into the current one.

This method takes an rvalue.

Parameters

sketch the sketch to merge into the current object

◆ get_k()

template<typename T , typename A >

uint32_t get_k ( ) const

inline

Returns the configured maximum sample size.

Returns: configured maximum sample size

◆ get_n()

template<typename T , typename A >

uint64_t get_n ( ) const

inline

Returns the number of items processed by the sketch, regardless of item weight.

Returns: count of items processed by the sketch

◆ get_cumulative_weight()

template<typename T , typename A >

double get_cumulative_weight ( ) const

inline

Returns the cumulative weight of items processed by the sketch.

Returns: cumulative weight of items seen

◆ get_c()

template<typename T , typename A >

double get_c ( ) const

inline

Returns the expected number of samples returned upon a call to get_result() or the creation of an iterator.

The number is a floating point value, where the fractional portion represents the probability of including a "partial item" from the sample.

The value C should be no larger than the sketch's configured value of k, although numerical precision limitations mean it may exceed k by double precision floating point error margins in certain cases.

Returns: The expected number of samples returned when querying the sketch

◆ is_empty()

template<typename T , typename A >

bool is_empty ( ) const

inline

Returns true if the sketch is empty.

Returns: empty flag

◆ get_allocator()

template<typename T , typename A >

A get_allocator ( ) const

Returns an instance of the allocator for this sketch.

Returns: allocator

◆ get_serialized_size_bytes()

template<typename T , typename A >

template<typename SerDe >

size_t get_serialized_size_bytes ( const SerDe & sd = SerDe() ) const

inline

Computes size needed to serialize the current state of the sketch.

Parameters

sd	instance of a SerDe

Returns: size in bytes needed to serialize this sketch

◆ serialize() [1/2]

template<typename T , typename A = std::allocator<T>>

template<typename SerDe = serde<T>>

vector_bytes serialize	(	unsigned	header_size_bytes = `0`,
		const SerDe &	sd = `SerDe()`
	)		const

This method serializes the sketch as a vector of bytes.

An optional header can be reserved in front of the sketch. It is a blank space of a given size. This header is used in Datasketches PostgreSQL extension.

Parameters

header_size_bytes	space to reserve in front of the sketch
sd	instance of a SerDe

◆ serialize() [2/2]

template<typename T , typename A >

template<typename SerDe >

void serialize	(	std::ostream &	os,
		const SerDe &	sd = `SerDe()`
	)		const

This method serializes the sketch into a given stream in a binary form.

Parameters

os	output stream
sd	instance of a SerDe

◆ deserialize() [1/2]

template<typename T , typename A = std::allocator<T>>

template<typename SerDe = serde<T>>

static ebpps_sketch deserialize	(	const void *	bytes,
		size_t	size,
		const SerDe &	sd = `SerDe()`,
		const A &	allocator = `A()`
	)

static

This method deserializes a sketch from a given array of bytes.

Parameters

bytes	pointer to the array of bytes
size	the size of the array
sd	instance of a SerDe
allocator	instance of an allocator

Returns: an instance of a sketch

◆ deserialize() [2/2]

template<typename T , typename A = std::allocator<T>>

template<typename SerDe = serde<T>>

static ebpps_sketch deserialize	(	std::istream &	is,
		const SerDe &	sd = `SerDe()`,
		const A &	allocator = `A()`
	)

static

This method deserializes a sketch from a given stream.

Parameters

is	input stream
sd	instance of a SerDe
allocator	instance of an allocator

Returns: an instance of a sketch

◆ to_string()

template<typename T , typename A >

string< A > to_string ( ) const

Prints a summary of the sketch.

Returns: the summary as a string

◆ items_to_string()

template<typename T , typename A >

string< A > items_to_string ( ) const

Prints the raw sketch items to a string.

Only works for type T with a defined std::ostream& operator<<(std::ostream&, const T&) and is kept separate from to_string() to allow compilation even if T does not have such an operator defined.

Returns: a string with the sketch items

◆ begin()

template<typename T , typename A >

ebpps_sample< T, A >::const_iterator begin ( ) const

Iterator pointing to the first item in the sketch.

If the sketch is empty, the returned iterator must not be dereferenced or incremented.

Returns: iterator pointing to the first item in the sketch

◆ end()

template<typename T , typename A >

ebpps_sample< T, A >::const_iterator end ( ) const

Iterator pointing to the past-the-end item in the sketch.

The past-the-end item is the hypothetical item that would follow the last item. It does not point to any item, and must not be dereferenced or incremented.

Returns: iterator pointing to the past-the-end item in the sketch

The documentation for this class was generated from the following files:

sampling/include/ebpps_sketch.hpp
sampling/include/ebpps_sketch_impl.hpp

Public Member Functions

Static Public Member Functions

Detailed Description

Constructor & Destructor Documentation

◆ ebpps_sketch()

Member Function Documentation

◆ update() [1/2]

◆ update() [2/2]

◆ merge() [1/2]

◆ merge() [2/2]

◆ get_k()

◆ get_n()

◆ get_cumulative_weight()

◆ get_c()

◆ is_empty()

◆ get_allocator()

◆ get_serialized_size_bytes()

◆ serialize() [1/2]

◆ serialize() [2/2]

◆ deserialize() [1/2]

◆ deserialize() [2/2]

◆ to_string()

◆ items_to_string()

◆ begin()

◆ end()