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From "Daniel Dai (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-1434) Allow casting relations to scalars
Date Fri, 09 Jul 2010 17:09:58 GMT

    [ https://issues.apache.org/jira/browse/PIG-1434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12886772#action_12886772
] 

Daniel Dai commented on PIG-1434:
---------------------------------

We may also add some sanity check, instead of just doing a limit.
{code}
C = foreach C generate CheckSingular(*);
Z = join X by 1, C by 1 using 'replicated';
Y = foreach Z generate X::$1/(long) C.count, X::$2-(long) C.max;
{code}

CheckSingular will check if C only have one record.

> 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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