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https://issues.apache.org/jira/browse/PIG-1718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12931304#action_12931304
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Santhosh Srinivasan commented on PIG-1718:
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This should be fixed as part of the semantics cleanup. The foreach allows the
specification of the type information when the current semantic is plain
aliasing.
> Cannot directly cast output of UDF
> ----------------------------------
>
> Key: PIG-1718
> URL: https://issues.apache.org/jira/browse/PIG-1718
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Affects Versions: 0.7.0
> Environment: Macbook Pro 6.2, Ubuntu 10.04 AMD64, CDH3 beta 3
> Reporter: Mike Dillon
> Priority: Minor
>
> I'm in the process of writing a suite of UDFs to deal with nested JSON data
> inside of Pig. In one case, I created a UDF of type EvalFunc<String> and
> wanted to use it like so:
> {code}
> RAW = load 'input.tsv' using PigStorage as ( id: int, json: chararray );
> IN = foreach RAW generate id, ExtractString(json, 'count') as count:int
> {code}
> When I do this, I get the following error:
> {quote}
> ERROR 1022: Type mismatch merging schema prefix. Field Schema: chararray.
> Other Field Schema: count: int
> {quote}
> I can work around it by adding another projection with just a cast (as
> below), but I'd prefer if the form I just first just worked.
> {code}
> RAW = load 'input.tsv' using PigStorage as ( id: int, json: chararray );
> MID = foreach RAW generate id, ExtractString(json, 'count') as count
> IN = foreach MID generate id, (int)count
> {code}
> I'd prefer not to have to have ExtractInteger extends EvalFun<Integer> if I
> can avoid it. In our case, it gets even more cumbersome because we want to
> have something like ExtractStringTuple extends EvalFunc<Tuple> that returns a
> tuple of strings without parsing the JSON over and over again:
> {code}
> RAW = load 'input.tsv' using PigStorage as ( id: int, json: chararray );
> IN = foreach RAW generate id, ExtractStringTuple(json, 'name', 'count',
> 'mean') as (name, count:int, mean:double);
> {code}
> As indicated, I have tested this with Pig 0.7.0. My apologies if this is
> already fixed in 0.8 since I was not able to test with a newer version.
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