VAR() Variance UDF
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                 Key: PIG-1150
                 URL: https://issues.apache.org/jira/browse/PIG-1150
             Project: Pig
          Issue Type: New Feature
    Affects Versions: 0.5.0
         Environment: UDF, written in Pig 0.5 contrib/
            Reporter: Russell Jurney
             Fix For: 0.5.0


I've implemented a UDF in Pig 0.5 that implements Algebraic and calculates 
variance in a distributed manner, based on the AVG() builtin.  It works by 
calculating the count, sum and sum of squares, as described here: 
http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#Parallel_algorithm

Is this a worthwhile contribution?  Taking the square root of this value using 
the contrib SQRT() function gives Standard Deviation, which is missing from Pig.

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