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From "Eric Gaudet (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-795) Command that selects a random sample of the rows, similar to LIMIT
Date Sat, 02 May 2009 01:31:30 GMT

     [ https://issues.apache.org/jira/browse/PIG-795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Eric Gaudet updated PIG-795:
----------------------------

    Attachment: sample3.diff

This is the implementation of the SAMPLE operator rewritten as FILTER by the query parser,
as suggested by Olga and Alan. It uses a new built-in function RANDOM(), copied from piggybank.
This patch also adds the unit test TestSample. 

I am unfamiliar with LogicalPlan crafting, so the code might not be the best. Please feel
free to clean it up.



> Command that selects a random sample of the rows, similar to LIMIT
> ------------------------------------------------------------------
>
>                 Key: PIG-795
>                 URL: https://issues.apache.org/jira/browse/PIG-795
>             Project: Pig
>          Issue Type: New Feature
>          Components: impl
>            Reporter: Eric Gaudet
>            Priority: Trivial
>         Attachments: sample2.diff, sample3.diff
>
>
> When working with very large data sets (imagine that!), running a pig script can take
time. It may be useful to run on a small subset of the data in some situations (eg: debugging
/ testing, or to get fast results even if less accurate.) 
> The command "LIMIT N" selects the first N rows of the data, but these are not necessarily
randomzed. A command "SAMPLE X" would retain the row only with the probability x%.
> Note: it is possible to implement this feature with FILTER BY and an UDF, but so is LIMIT,
and limit is built-in.

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