org.apache.pig.builtin

Class CubeDimensions

java.lang.Object

org.apache.pig.EvalFunc<DataBag>

org.apache.pig.builtin.CubeDimensions

public class CubeDimensions
extends EvalFunc<DataBag>

Produces a DataBag with all combinations of the argument tuple members as in a data cube. Meaning, (a, b, c) will produce the following bag:

 { (a, b, c), (null, null, null), (a, b, null), (a, null, c),
   (a, null, null), (null, b, c), (null, null, c), (null, b, null) }
 

The "all" marker is null by default, but can be set to an arbitrary string by invoking a constructor (via a DEFINE). The constructor takes a single argument, the string you want to represent "all".

Usage goes something like this:

 events = load '/logs/events' using EventLoader() as (lang, event, app_id);
 cubed = foreach x generate
   FLATTEN(piggybank.CubeDimensions(lang, event, app_id))
     as (lang, event, app_id),
   measure;
 cube = foreach (group cubed
                 by (lang, event, app_id) parallel $P)
        generate
   flatten(group) as (lang, event, app_id),
   COUNT_STAR(cubed),
   SUM(measure);
 store cube into 'event_cube';
 

Note: doing this with non-algebraic aggregations on large data can result in very slow reducers, since one of the groups is going to get all the records in your relation.

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
CubeDimensions()
CubeDimensions(String allMarker)

Method Summary

Modifier and Type	Method and Description
boolean	allowCompileTimeCalculation() Whether the UDF should be evaluated at compile time if all inputs are constant.
static void	convertNullToUnknown(Tuple tuple)
DataBag	exec(Tuple tuple) 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, getLoadCaster, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, needEndOfAllInputProcessing, progress, setEndOfAllInput, 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

CubeDimensions

public CubeDimensions()

CubeDimensions

public CubeDimensions(String allMarker)

Method Detail

exec

public DataBag exec(Tuple tuple)
             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<DataBag>

Parameters:

tuple - the Tuple to be processed.

Returns:

result, of type T.

Throws:

IOException

convertNullToUnknown

public static void convertNullToUnknown(Tuple tuple)
                                 throws ExecException

Throws:

ExecException

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