org.apache.pig.builtin

Class INVERSEMAP

java.lang.Object

org.apache.pig.EvalFunc<java.util.Map>

org.apache.pig.builtin.INVERSEMAP

public class INVERSEMAP
extends EvalFunc<java.util.Map>

This UDF accepts a Map as input with values of any primitive data type.
UDF swaps keys with values and returns the new inverse Map.
Note in case original values are non-unique, the resulting Map would
contain String Key -> DataBag of values. Here the bag of values is composed
of the original keys having the same value.

 Note: 1. UDF accepts Map with Values of primitive data type
       2. UDF returns Map
 
 grunt> cat 1data
 [open#1,1#2,11#2]
 [apache#2,3#4,12#24]

 

 grunt> a = load 'data' as (M:[int]);
 grunt> b = foreach a generate INVERSEMAP($0);

 grunt> dump b;
 ([2#{(1),(11)},apache#{(open)}])
 ([hadoop#{(apache),(12)},4#{(3)}])
 
 

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
INVERSEMAP()

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.
java.util.Map	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

INVERSEMAP

public INVERSEMAP()

Method Detail

exec

public java.util.Map 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<java.util.Map>

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<java.util.Map>

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<java.util.Map>

Returns:

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