datafu.pig.sessions

Class SessionCount

java.lang.Object

org.apache.pig.EvalFunc<T>

org.apache.pig.AccumulatorEvalFunc<java.lang.Long>

datafu.pig.sessions.SessionCount

All Implemented Interfaces:

org.apache.pig.Accumulator<java.lang.Long>

public class SessionCount
extends org.apache.pig.AccumulatorEvalFunc<java.lang.Long>

Performs a count of events, ignoring events which occur within the same time window.

This is useful for tasks such as counting the number of page views per user since it: a) prevent reloads and go-backs from overcounting actual views b) captures the notion that views across multiple sessions are more meaningful

Input must be sorted ascendingly by time for this UDF to work.

Example:

 %declare TIME_WINDOW  10m
 
 define SessionCount datafu.pig.sessions.SessionCount('$TIME_WINDOW');
 
 views = LOAD 'views' as (user_id:int, page_id:int, time:chararray);
 views_grouped = GROUP views by (user_id, page_id);
 view_counts = FOREACH views_grouped { 
   views = order views by time;
   generate group.user_id as user_id, 
            group.page_id as page_id, 
            SessionCount(views.(time)) as count; }
 
 

Nested Class Summary

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

org.apache.pig.EvalFunc.SchemaType

Field Summary

Fields inherited from class org.apache.pig.EvalFunc

log, pigLogger, reporter, returnType

Constructor Summary

Constructors

Constructor and Description
SessionCount(java.lang.String timeSpec)

Method Summary

Methods

Modifier and Type	Method and Description
void	accumulate(org.apache.pig.data.Tuple input)
void	cleanup()
java.lang.Long	getValue()

Methods inherited from class org.apache.pig.AccumulatorEvalFunc

exec

Methods inherited from class org.apache.pig.EvalFunc

allowCompileTimeCalculation, finish, getArgToFuncMapping, getCacheFiles, getInputSchema, getLogger, getPigLogger, getReporter, getReturnType, getSchemaName, getSchemaType, getShipFiles, isAsynchronous, outputSchema, 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

SessionCount

public SessionCount(java.lang.String timeSpec)

Method Detail

accumulate

public void accumulate(org.apache.pig.data.Tuple input)
                throws java.io.IOException

Specified by:

accumulate in interface org.apache.pig.Accumulator<java.lang.Long>

Specified by:

accumulate in class org.apache.pig.AccumulatorEvalFunc<java.lang.Long>

Throws:

java.io.IOException

getValue

public java.lang.Long getValue()

Specified by:

getValue in interface org.apache.pig.Accumulator<java.lang.Long>

Specified by:

getValue in class org.apache.pig.AccumulatorEvalFunc<java.lang.Long>

cleanup

public void cleanup()

Specified by:

cleanup in interface org.apache.pig.Accumulator<java.lang.Long>

Specified by:

cleanup in class org.apache.pig.AccumulatorEvalFunc<java.lang.Long>