org.apache.pig.builtin

Class KEYSET

java.lang.Object

org.apache.pig.EvalFunc<DataBag>

org.apache.pig.builtin.KEYSET

public class KEYSET
extends EvalFunc<DataBag>

This UDF takes a Map and returns a Bag containing the keyset.

 
 grunt> cat data
 [open#apache,1#2,11#2]
 [apache#hadoop,3#4,12#hadoop]

 grunt> a = load 'data' as (M:[]);
 grunt> b = foreach a generate KEYSET($0);
 grunt> dump b;
 ({(open),(1),(11)})
 ({(3),(apache),(12)})
 
 

Nested Class Summary

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

EvalFunc.SchemaType

Field Summary

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

Constructors

Constructor and Description
KEYSET()

Method Summary

Methods

Modifier and Type	Method and Description
boolean	allowCompileTimeCalculation() Whether the UDF should be evaluated at compile time if all inputs are constant.
DataBag	exec(Tuple input) This callback method must be implemented by all subclasses.
Schema	outputSchema(Schema input) Report the schema of the output of this UDF.

Methods inherited from class org.apache.pig.EvalFunc

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

Methods inherited from class java.lang.Object

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

Constructor Detail

KEYSET

public KEYSET()

Method Detail

exec

public DataBag exec(Tuple input)
             throws java.io.IOException

Description copied from class: EvalFunc

This callback method must be implemented by all subclasses. This is the method that will be invoked on every Tuple of a given dataset. Since the dataset may be divided up in a variety of ways the programmer should not make assumptions about state that is maintained between invocations of this method.

Specified by:

exec in class EvalFunc<DataBag>

Parameters:

input - the Tuple to be processed.

Returns:

result, of type T.

Throws:

java.io.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

allowCompileTimeCalculation

public boolean allowCompileTimeCalculation()

Description copied from class: EvalFunc

Whether the UDF should be evaluated at compile time if all inputs are constant. This is applicable for most UDF, however, if a UDF will access hdfs file which is not available at compile time, it has to be false

Overrides:

allowCompileTimeCalculation in class EvalFunc<DataBag>

Returns:

Whether or not compile time calculation is allowed, default to false to ensure legacy UDF will get the right behavior