[jira] [Commented] (SPARK-4476) Use MapType for dict in json which has unique keys in each row.

["Yin Huai (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SPARK-4476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14495623#comment-14495623 ] 

Yin Huai commented on SPARK-4476:
---------------------------------

I will try to find a time to rebase my old patch.

> Use MapType for dict in json which has unique keys in each row.
> ---------------------------------------------------------------
>
>                 Key: SPARK-4476
>                 URL: https://issues.apache.org/jira/browse/SPARK-4476
>             Project: Spark
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Davies Liu
>            Assignee: Yin Huai
>            Priority: Critical
>
> For the jsonRDD like this: 
> {code}
> """ {a: 1} """
> """ {b: 2} """
> """ {c: 3} """
> """ {d: 4} """
> """ {e: 5} """
> {code}
> It will create a StructType with 5 fileds in it, each field come from a different row. It will be a problem if the RDD is large. A StructType with thousands or millions fields is hard to play with (will cause stack overflow during serialization).
> It should be MapType for this case. We need a clear rule to decide StructType or MapType will be used for dict in json data. 
> cc [~yhuai] [~marmbrus]



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