org.apache.pig.builtin
Class COV

java.lang.Object
  org.apache.pig.EvalFunc<DataBag>
      org.apache.pig.builtin.COV

All Implemented Interfaces:

Algebraic

public class COV
extends EvalFunc<DataBag>
implements Algebraic

Computes the covariance between sets of data. The returned value will be a bag which will contain a tuple for each combination of input schema and inside tuple we will have two schema name and covariance between those two schemas. A = load 'input.xml' using PigStorage(':');
B = group A all;
D = foreach B generate group,COV(A.$0,A.$1,A.$2);

Nested Class Summary

static class	COV.Final
static class	COV.Initial
static class	COV.Intermed

Nested classes/interfaces inherited from class org.apache.pig.EvalFunc

EvalFunc.SchemaType

Field Summary

protected Vector<String>

schemaName

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

COV()

COV(String... schemaName)

Method Summary

protected static Tuple	combine(DataBag values) combine results of different data chunk
protected static Tuple	computeAll(DataBag first, DataBag second) compute sum(XY), sum(X), sum(Y) from given data sets
DataBag	exec(Tuple input) Function to compute covariance between data sets.
String	getFinal() Get the final function.
String	getInitial() Get the initial function.
String	getIntermed() Get the intermediate function.
Schema	outputSchema(Schema input) Report the schema of the output of this UDF.
String	toString() Function to return argument of constructor as string.

Methods inherited from class org.apache.pig.EvalFunc

finish, getArgToFuncMapping, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, isAsynchronous, progress, setInputSchema, setPigLogger, setReporter, setUDFContextSignature, warn

Methods inherited from class java.lang.Object

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

Field Detail

schemaName

protected Vector<String> schemaName

Constructor Detail

COV

public COV()

COV

public COV(String... schemaName)

Method Detail

exec

public DataBag exec(Tuple input)
             throws IOException

Function to compute covariance between data sets.

Specified by:

exec in class EvalFunc<DataBag>

Parameters:

input - input tuple which contains data sets.

Returns:

output output dataBag which contain covariance between each pair of data sets.

Throws:

IOException

toString

public String toString()

Function to return argument of constructor as string. It append ( and ) at starting and end or argument respectively. If default constructor is called is returns empty string.

Overrides:

toString in class Object

Returns:

argument of constructor

getInitial

public String getInitial()

Description copied from interface: Algebraic

Get the initial function.

Specified by:

getInitial in interface Algebraic

Returns:

A function name of f_init. f_init should be an eval func. The return type of f_init.exec() has to be Tuple

getIntermed

public String getIntermed()

Description copied from interface: Algebraic

Get the intermediate function.

Specified by:

getIntermed in interface Algebraic

Returns:

A function name of f_intermed. f_intermed should be an eval func. The return type of f_intermed.exec() has to be Tuple

getFinal

public String getFinal()

Description copied from interface: Algebraic

Get the final function.

Specified by:

getFinal in interface Algebraic

Returns:

A function name of f_final. f_final should be an eval func parametrized by the same datum as the eval func implementing this interface.

combine

protected static Tuple combine(DataBag values)
                        throws IOException

combine results of different data chunk

Parameters:

values - DataBag containing partial results computed on different data chunks

Returns:

output Tuple containing combined data

Throws:

IOException

computeAll

protected static Tuple computeAll(DataBag first,
                                  DataBag second)
                           throws IOException

compute sum(XY), sum(X), sum(Y) from given data sets

Parameters:

first - DataBag containing first data set

second - DataBag containing second data set

Returns:

tuple containing sum(XY), sum(X), sum(Y)

Throws:

IOException

outputSchema

public Schema outputSchema(Schema input)

Description copied from class: EvalFunc

Report the schema of the output of this UDF. Pig will make use of this in error checking, optimization, and planning. The schema of input data to this UDF is provided.

The default implementation interprets the OutputSchema annotation, if one is present. Otherwise, it returns null (no known output schema).

Overrides:

outputSchema in class EvalFunc<DataBag>

Parameters:

input - Schema of the input

Returns:

Schema of the output