Package org.apache.datasketches.theta

Class CompactSketch

java.lang.Object

org.apache.datasketches.theta.Sketch

org.apache.datasketches.theta.CompactSketch

public abstract class CompactSketch
extends Sketch

The parent class of all the CompactSketches. CompactSketches are never created directly. They are created as a result of the compact() method of an UpdateSketch or as a result of a getResult() of a SetOperation.

A CompactSketch is the simplest form of a Theta Sketch. It consists of a compact list (i.e., no intervening spaces) of hash values, which may be ordered or not, a value for theta and a seed hash. A CompactSketch is read-only, and the space required when stored is only the space required for the hash values and 8 to 24 bytes of preamble. An empty CompactSketch consumes only 8 bytes.

Author:

Lee Rhodes

Constructor Summary

Constructors

Constructor	Description
CompactSketch()

Method Summary

Modifier and Type	Method	Description
abstract CompactSketch	compact(boolean dstOrdered, org.apache.datasketches.memory.WritableMemory dstMem)	Convert this sketch to a new CompactSketch of the chosen order and direct or on the heap.
int	getCompactBytes()	Returns the number of storage bytes required for this Sketch if its current state were compacted.
Family	getFamily()	Returns the Family that this sketch belongs to
boolean	isCompact()	Returns true if this sketch is in compact form.

Methods inherited from class org.apache.datasketches.theta.Sketch

compact, getCountLessThanThetaLong, getCurrentBytes, getEstimate, getLowerBound, getMaxCompactSketchBytes, getMaxUpdateSketchBytes, getRetainedEntries, getRetainedEntries, getSerializationVersion, getTheta, getThetaLong, getUpperBound, hasMemory, heapify, heapify, isDirect, isEmpty, isEstimationMode, isOrdered, isSameResource, iterator, toByteArray, toString, toString, toString, toString, wrap, wrap

Methods inherited from class java.lang.Object

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

Constructor Details

CompactSketch

public CompactSketch()

Method Details

compact

public abstract CompactSketch compact(boolean dstOrdered, org.apache.datasketches.memory.WritableMemory dstMem)

Description copied from class: Sketch

Convert this sketch to a new CompactSketch of the chosen order and direct or on the heap.

If this sketch is already in the proper form, this operation returns this, otherwise, this method returns a new CompactSketch of the proper form.

If this sketch is a type of UpdateSketch, the compacting process converts the hash table of the UpdateSketch to a simple list of the valid hash values. Any hash values of zero or equal-to or greater than theta will be discarded. The number of valid values remaining in the CompactSketch depends on a number of factors, but may be larger or smaller than Nominal Entries (or k). It will never exceed 2k. If it is critical to always limit the size to no more than k, then rebuild() should be called on the UpdateSketch prior to calling this method.

A CompactSketch is always immutable.

Specified by:

compact in class Sketch

Parameters:

dstOrdered - See Destination Ordered

dstMem - See Destination Memory.

Returns:

this sketch as a CompactSketch in the chosen form

getCompactBytes

public int getCompactBytes()

Description copied from class: Sketch

Returns the number of storage bytes required for this Sketch if its current state were compacted. It this sketch is already in the compact form this is equivalent to calling Sketch.getCurrentBytes().

Specified by:

getCompactBytes in class Sketch

Returns:

number of compact bytes

getFamily

public Family getFamily()

Description copied from class: Sketch

Returns the Family that this sketch belongs to

Specified by:

getFamily in class Sketch

Returns:

the Family that this sketch belongs to

isCompact

public boolean isCompact()

Description copied from class: Sketch

Returns true if this sketch is in compact form.

Specified by:

isCompact in class Sketch

Returns:

true if this sketch is in compact form.