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https://issues.apache.org/jira/browse/PIG-795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Eric Gaudet updated PIG-795:
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Attachment: sample2.diff
This patch implements the SAMPLE command. It basically add a random sample mode
to the LIMIT class.
The syntax is like LIMIT: "a = SAMPLE x", where x is an integer and 0<=x<=100.
Each row will be selected if rand()<(x/100).
Example:
a = LOAD 'mybigdata'
b = SAMPLE 5
...
will select 5% of the data.
> 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
>
>
> 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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