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https://issues.apache.org/jira/browse/PIG-5085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15870970#comment-15870970
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Rohini Palaniswamy commented on PIG-5085:
-----------------------------------------
Patch is good. Just 2 minor comments on documentation.
1) Can skip detail here as explanation for each follows immediately.
Flatten un-nests tuples as well as bags. It can also be used on maps to
break down the key-value pair structure into a key and a value part within a
tuple. -> Flatten un-nests tuples, bags and maps.
2) Can make the map section similar to previous paragraph on bags for easy
reading. Would be good to have details on how to reference them.
{code}
<p>For maps, flatten creates a tuple with two fields containing the key and
value.
If we have a map field named kvpair with input as (m[k1#v1, k2#v2]) and we
apply GENERATE flatten(kvpair), it will generate two tuples (k1,v1) and (k1,v2)
which can be accessed as kvpair::key and kvpair::value.
When there are additional projections in the expression, a cross product
will happen similar to bags.
For example, if we apply the expression GENERATE $0, flatten($1) to the
input tuple (a, m[k1#1, k2#2, k3#3]), we will see (a,k1,1), (a,k2,2) and
(a,k3,3) as the result.</p>
{code}
> Support FLATTEN of maps
> -----------------------
>
> Key: PIG-5085
> URL: https://issues.apache.org/jira/browse/PIG-5085
> Project: Pig
> Issue Type: New Feature
> Reporter: Rohini Palaniswamy
> Assignee: Adam Szita
> Fix For: 0.17.0
>
> Attachments: PIG-5085.0.patch, PIG-5085.1.patch
>
>
> I have come across users asking for this quite a few times. Don't see why
> we should not support it with FLATTEN instead of users having to write a UDF
> for that
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