org.apache.pig.builtin
Class INVERSEMAP

java.lang.Object
  extended by org.apache.pig.EvalFunc<Map>
      extended by org.apache.pig.builtin.INVERSEMAP

public class INVERSEMAP
extends EvalFunc<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
INVERSEMAP()
           
 
Method Summary
 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, 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 Map exec(Tuple input)
         throws 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<Map>
Parameters:
input - the Tuple to be processed.
Returns:
result, of type T.
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<Map>
Parameters:
input - Schema of the input
Returns:
Schema of the output


Copyright © 2007-2012 The Apache Software Foundation