[jira] [Commented] (DATAFU-130) Add left outer join macro described in the DataFu guide

["Eyal Allweil (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DATAFU-130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16169225#comment-16169225 ] 

Eyal Allweil commented on DATAFU-130:
-------------------------------------

I think this is a good Jira issue to put in the [Apache Help Wanted site|https://helpwanted.apache.org/]. If there's no objection, I'll add it there.

> Add left outer join macro described in the DataFu guide
> -------------------------------------------------------
>
>                 Key: DATAFU-130
>                 URL: https://issues.apache.org/jira/browse/DATAFU-130
>             Project: DataFu
>          Issue Type: New Feature
>            Reporter: Eyal Allweil
>              Labels: macro, newbie
>
> In our [guide|http://datafu.incubator.apache.org/blog/2013/09/04/datafu-1-0.html], a macro is described for making a three-way left outer join conveniently. We can add this macro to DataFu to make it even easier to use.
> The macro's code is as follows:
> {noformat}
> DEFINE left_outer_join(relation1, key1, relation2, key2, relation3, key3) returns joined {
>   cogrouped = COGROUP $relation1 BY $key1, $relation2 BY $key2, $relation3 BY $key3;
>   $joined = FOREACH cogrouped GENERATE
>     FLATTEN($relation1),
>     FLATTEN(EmptyBagToNullFields($relation2)),
>     FLATTEN(EmptyBagToNullFields($relation3));
> }
> (we would obviously want to add a test for this, too)
> {noformat}



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