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https://issues.apache.org/jira/browse/DATAFU-130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16732684#comment-16732684
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Matthew Hayes commented on DATAFU-130:
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Patch looks good to me except I think we should append a number to
left_outer_join to indicate the number of relations so we can add more left
join macros in the future. Maybe call it left_outer_join2 since you are
joining with 2 other relations? We could also add a left_outer_join and
left_outer_join3. Thoughts?
> 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
> Assignee: Eyal Allweil
> Priority: Major
> Labels: macro, newbie
> Attachments: DATAFU-130.patch
>
>
> 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));
> }
> {noformat}
> (we would obviously want to add a test for this, too)
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