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https://issues.apache.org/jira/browse/PIG-1150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12847600#action_12847600
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Russell Jurney commented on PIG-1150:
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Yes, this sounds like the thing to do :)
On Tue, Mar 16, 2010 at 5:29 PM, Dmitriy V. Ryaboy (JIRA)
> VAR() Variance UDF
> ------------------
>
> 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: 0.7.0
>
> Attachments: var.patch
>
>
> 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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