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https://issues.apache.org/jira/browse/HIVE-2085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13013549#comment-13013549
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Edward Capriolo commented on HIVE-2085:
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The best way to currently learn about these features is to look through the
unit tests, code, and .q files. There other UDFs like atan easy to follow.
There is a UDFT for example that splits a URL into parts. Looking at the
split() or case() UDF's give you an idea of some of the more complex things
that can be done. Looking at struct() or list() udfs shows you a lot about how
to use object inspectors to detect and return different types. If you want to
come on IRC I can help with specific questions.
> Document GenericUD(A|T)F
> ------------------------
>
> Key: HIVE-2085
> URL: https://issues.apache.org/jira/browse/HIVE-2085
> Project: Hive
> Issue Type: Improvement
> Components: Documentation
> Reporter: Lars Francke
> Priority: Minor
>
> GenericUDFs are very poorly documented, this includes everything they relate
> to:
> * ObjectInspector (JavaDoc not really helpful for someone not familiar with
> Hive)
> * ObjectInspectorFactory
> * ObjectInspectorConverters
> * ...
> An example would help as well as a unit test for one of the built in
> GenericUDFs. Writing a normal UDF is pretty well documented but GenericUDFs
> (and UDTF/UDAF) require more knowledge about the inner workings of Hive and
> that could be documented better.
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