Package com.arcadedb.query.sql.function.stat

Class SQLFunctionVariance

java.lang.Object

com.arcadedb.query.sql.function.SQLFunctionAbstract

com.arcadedb.query.sql.function.stat.SQLFunctionVariance

All Implemented Interfaces:

SQLFunction

Direct Known Subclasses:

SQLFunctionStandardDeviation

public class SQLFunctionVariance
extends SQLFunctionAbstract

Compute the variance estimation for a given field.

This class uses the Weldford's algorithm (presented in Donald Knuth's Art of Computer Programming) to avoid multiple distribution values' passes. When executed in distributed mode it uses the Chan at al. pairwise variance algorithm to merge the results.

References

• Cook, John D. Accurately computing running variance.
• Knuth, Donald E. (1998) The Art of Computer Programming, Volume 2: Seminumerical Algorithms, 3rd Edition.
• Welford, B. P. (1962) Note on a method for calculating corrected sums of squares and products. Technometrics
• Chan, Tony F.; Golub, Gene H.; LeVeque, Randall J. (1979), Parallel Algorithm.

Author:

Fabrizio Fortino

Field Summary

Fields

Modifier and Type	Field	Description
static String	NAME

Fields inherited from class com.arcadedb.query.sql.function.SQLFunctionAbstract

name

Constructor Summary

Constructors

Constructor	Description
SQLFunctionVariance()
SQLFunctionVariance(String iName, int iMinParams, int iMaxParams)

Method Summary

Modifier and Type	Method	Description
boolean	aggregateResults()	A function can make calculation on several records before returning a result.
Object	execute(Object iThis, Identifiable iCurrentRecord, Object iCurrentResult, Object[] iParams, CommandContext iContext)	Process a record.
Object	getResult()	Only called when function aggregates results after all records have been passed to the function.
String	getSyntax()	Returns a convenient SQL String representation of the function.

Methods inherited from class com.arcadedb.query.sql.function.SQLFunctionAbstract

config, getName, toString

Methods inherited from class java.lang.Object

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

Field Detail

NAME

public static final String NAME

See Also:

Constant Field Values

Constructor Detail

SQLFunctionVariance

public SQLFunctionVariance()

SQLFunctionVariance

public SQLFunctionVariance(String iName,
                           int iMinParams,
                           int iMaxParams)

Method Detail

execute

public Object execute(Object iThis,
                      Identifiable iCurrentRecord,
                      Object iCurrentResult,
                      Object[] iParams,
                      CommandContext iContext)

Description copied from interface: SQLFunction

Process a record.

iCurrentRecord - : current record

iCurrentResult - TODO

iParams - : function parameters, number is ensured to be within minParams and maxParams.

iContext - : object calling this function

Returns:

function result, can be null. Special cases : can be null if function aggregate results, can be null if function filter results : this mean result is excluded

aggregateResults

public boolean aggregateResults()

Description copied from interface: SQLFunction

A function can make calculation on several records before returning a result.

Example of such function : sum, count, max, min ...

The final result of the aggregation is obtained by calling SQLFunction.getResult()

Specified by:

aggregateResults in interface SQLFunction

Overrides:

aggregateResults in class SQLFunctionAbstract

Returns:

true if function aggregate results

getResult

public Object getResult()

Description copied from interface: SQLFunction

Only called when function aggregates results after all records have been passed to the function.

Specified by:

getResult in interface SQLFunction

Overrides:

getResult in class SQLFunctionAbstract

Returns:

Aggregation result

getSyntax

public String getSyntax()

Description copied from interface: SQLFunction

Returns a convenient SQL String representation of the function.

Example :

  myFunction( param1, param2, [optionalParam3])
 

This text will be used in exception messages.

Returns:

String , never null.