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Posted to dev@pig.apache.org by "Eric Gaudet (JIRA)" <ji...@apache.org> on 2009/05/01 01:23:31 UTC
[jira] Updated: (PIG-795) Command that selects a random sample of
the rows, similar to LIMIT
[ https://issues.apache.org/jira/browse/PIG-795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Eric Gaudet updated PIG-795:
----------------------------
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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