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From "Dmitriy V. Ryaboy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-1434) Allow casting relations to scalars
Date Fri, 02 Jul 2010 17:54:51 GMT

    [ https://issues.apache.org/jira/browse/PIG-1434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12884755#action_12884755
] 

Dmitriy V. Ryaboy commented on PIG-1434:
----------------------------------------

Richard,
In my opinion -- Yes in principle, but not as a replacement for this. 
Cross is dangerous, I would rather have a constrained "implicit scalar tuple" that people
use for the common case, and leave something like a replicated cross for power users (and
then not limit it to number of rows in replicated relation).

Agreed with not constraining this feature on the frontend, failing at runtime instead. 

> Allow casting relations to scalars
> ----------------------------------
>
>                 Key: PIG-1434
>                 URL: https://issues.apache.org/jira/browse/PIG-1434
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Olga Natkovich
>            Assignee: Aniket Mokashi
>             Fix For: 0.8.0
>
>         Attachments: scalarImpl.patch
>
>
> This jira is to implement a simplified version of the functionality described in https://issues.apache.org/jira/browse/PIG-801.
> The proposal is to allow casting relations to scalar types in foreach.
> Example:
> A = load 'data' as (x, y, z);
> B = group A all;
> C = foreach B generate COUNT(A);
> .....
> X = ....
> Y = foreach X generate $1/(long) C;
> Couple of additional comments:
> (1) You can only cast relations including a single value or an error will be reported
> (2) Name resolution is needed since relation X might have field named C in which case
that field takes precedence.
> (3) Y will look for C closest to it.
> Implementation thoughts:
> The idea is to store C into a file and then convert it into scalar via a UDF. I believe
we already have a UDF that Ben Reed contributed for this purpose. Most of the work would be
to update the logical plan to
> (1) Store C
> (2) convert the cast to the UDF

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