Package com.orientechnologies.orient.core.sql.functions.stat

Class OSQLFunctionVariance

java.lang.Object

com.orientechnologies.orient.core.sql.functions.OSQLFunctionAbstract

com.orientechnologies.orient.core.sql.functions.stat.OSQLFunctionVariance

All Implemented Interfaces:

OSQLFunction

Direct Known Subclasses:

OSQLFunctionStandardDeviation

public class OSQLFunctionVariance
extends OSQLFunctionAbstract

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 final String	NAME

Fields inherited from class com.orientechnologies.orient.core.sql.functions.OSQLFunctionAbstract

maxParams, minParams, name

Constructor Summary

Constructors

Constructor	Description
OSQLFunctionVariance()
OSQLFunctionVariance(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, OIdentifiable iCurrentRecord, Object iCurrentResult, Object[] iParams, OCommandContext iContext)	Process a record.
Object	getResult(OCommandContext ctx)	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.
Object	mergeDistributedResult(List<Object> resultsToMerge)	This method correspond to distributed query execution

Methods inherited from class com.orientechnologies.orient.core.sql.functions.OSQLFunctionAbstract

config, filterResult, getDatabase, getDistributedStorageId, getMaxParams, getMinParams, getName, getSingleItem, getSingleProperty, returnDistributedResult, setResult, shouldMergeDistributedResult, toString

Methods inherited from class java.lang.Object

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

Field Details

NAME

public static final String NAME

See Also:

• Constant Field Values

Constructor Details

OSQLFunctionVariance

public OSQLFunctionVariance()

OSQLFunctionVariance

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

Method Details

execute

public Object execute(Object iThis,
 OIdentifiable iCurrentRecord,
 Object iCurrentResult,
 Object[] iParams,
 OCommandContext iContext)

Description copied from interface: OSQLFunction

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: OSQLFunction

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 obtain by calling OSQLFunction.getResult(OCommandContext)

Specified by:

aggregateResults in interface OSQLFunction

Overrides:

aggregateResults in class OSQLFunctionAbstract

Returns:

true if function aggregate results

getResult

public Object getResult(OCommandContext ctx)

Description copied from interface: OSQLFunction

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

Specified by:

getResult in interface OSQLFunction

Overrides:

getResult in class OSQLFunctionAbstract

Parameters:

ctx - TODO

Returns:

Aggregation result

mergeDistributedResult

public Object mergeDistributedResult(List<Object> resultsToMerge)

Description copied from interface: OSQLFunction

This method correspond to distributed query execution

Specified by:

mergeDistributedResult in interface OSQLFunction

Overrides:

mergeDistributedResult in class OSQLFunctionAbstract

Parameters:

resultsToMerge - is the results that comes from different nodes

Returns:

is the valid merged result

getSyntax

public String getSyntax()

Description copied from interface: OSQLFunction

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.