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https://issues.apache.org/jira/browse/PIG-1876?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13004858#comment-13004858
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Daniel Dai commented on PIG-1876:
---------------------------------
Review notes: https://reviews.apache.org/r/472/
> Typed map for Pig
> -----------------
>
> Key: PIG-1876
> URL: https://issues.apache.org/jira/browse/PIG-1876
> Project: Pig
> Issue Type: New Feature
> Components: impl
> Reporter: Daniel Dai
> Assignee: Daniel Dai
> Fix For: 0.9.0
>
> Attachments: PIG-1876-1.patch, PIG-1876-2.patch, PIG-1876_3.patch
>
>
> Currently Pig map type is untyped, which means map value is always of
> bytearray(ie. unknown) type. In PIG-1277, we allow unknown type to be a
> shuffle key, which somewhat relieve the problem. However, typed map is still
> beneficial in that:
> 1. User can make semantic use of the map value type. Currently, user need to
> explicitly cast map value, which is ugly
> 2. Though PIG-1277 allow unknown type be a shuffle key, the performance
> suffers. We don't have a raw comparator for the unknown type, instead, we
> need to instantiate the value object and invoke its comparator
> Here is proposed syntax for typed map:
> map[type]
> Typed map can be used in place of untyped map could occur. For example:
> a = load '1.txt' as(map[int]);
> b = foreach a generate (map[(i:int)])a0; - - Map value is tuple
> b = stream a through `cat` as (m:map[{(i:int,j:chararray)}]); - - Map value
> is bag
> MapLookup a typed map will result datatype of map value.
> a = load '1.txt' as(map[int]);
> b = foreach a generate $0#'key';
> Schema for b:
> b: {int}
> The behavior of untyped map will remain the same.
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