Class VarSAggregator<V extends Number>

java.lang.Object

org.apache.derby.impl.sql.execute.VarPAggregator<V>

org.apache.derby.impl.sql.execute.VarSAggregator<V>

All Implemented Interfaces:

Externalizable, Serializable, Aggregator<V, Double, VarPAggregator<V>>

Direct Known Subclasses:

StdDevSAggregator

public class VarSAggregator<V extends Number>
extends VarPAggregator<V>

This class implements the SQL Standard VAR_SAMP() aggregator, computing the variance over a sample. It uses the IBM formula described here:

[ sum(xi2) - sum(xi)2/n ]/(n-1)

where

n is the number of items in the population
x1 ... xn are the items in the population

See Also:

• Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class VarPAggregator

VarPAggregator.Sums

Field Summary

Fields

Modifier and Type	Field	Description
private static final long	serialVersionUID

Fields inherited from class VarPAggregator

count, sums

Constructor Summary

Constructors

Constructor	Description
VarSAggregator()

Method Summary

Modifier and Type	Method	Description
protected Double	computeVar()

Methods inherited from class VarPAggregator

accumulate, init, merge, readExternal, terminate, writeExternal

Methods inherited from class Object

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

Field Details

serialVersionUID

private static final long serialVersionUID

See Also:

• Constant Field Values

Constructor Details

VarSAggregator

public VarSAggregator()

Method Details

computeVar

protected Double computeVar()

Overrides:

computeVar in class VarPAggregator<V extends Number>