org.apache.datasketches.theta

Class CompactSketch

java.lang.Object

org.apache.datasketches.theta.Sketch

org.apache.datasketches.theta.CompactSketch

Direct Known Subclasses:

SingleItemSketch

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 and Description
CompactSketch()

Method Summary

Modifier and Type	Method and Description
CompactSketch	compact() Converts this sketch to an ordered CompactSketch on the Java heap.
CompactSketch	compact(boolean dstOrdered, org.apache.datasketches.memory.WritableMemory dstMem) Convert this sketch to a CompactSketch in the chosen form.
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

getCountLessThanTheta, 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 Detail

CompactSketch

public CompactSketch()

Method Detail

compact

public CompactSketch compact()

Description copied from class: Sketch

Converts this sketch to an ordered CompactSketch on the Java heap.

If this sketch is already in compact form this operation returns this.

Specified by:

compact in class Sketch

Returns:

this sketch as an ordered CompactSketch on the Java heap.

compact

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

Description copied from class: Sketch

Convert this sketch to a CompactSketch in the chosen form.

If this sketch is already in compact form this operation returns this.

Otherwise, this compacting process converts the hash table form of an UpdateSketch to a simple list of the valid hash values from the hash table. Any hash values equal to or greater than theta will be discarded. The number of valid values remaining in the Compact Sketch 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 this.

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

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.