[jira] [Commented] (SPARK-18541) Add pyspark.sql.Column.aliasWithMetadata to allow dynamic metadata management in pyspark SQL API

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

    [ https://issues.apache.org/jira/browse/SPARK-18541?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15695922#comment-15695922 ] 

holdenk commented on SPARK-18541:
---------------------------------

Making it easier for PySpark SQL users to specify metadata sounds interesting/useful. I'd probably try and choose something closer to the scala API (e.g. implement `as` instead of `aliasWithMetadata`). What do [~davies] / [~marmbrus] think?

> Add pyspark.sql.Column.aliasWithMetadata to allow dynamic metadata management in pyspark SQL API
> ------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-18541
>                 URL: https://issues.apache.org/jira/browse/SPARK-18541
>             Project: Spark
>          Issue Type: Improvement
>          Components: PySpark, SQL
>    Affects Versions: 2.0.2
>         Environment: all
>            Reporter: Shea Parkes
>            Priority: Minor
>              Labels: newbie
>   Original Estimate: 24h
>  Remaining Estimate: 24h
>
> In the Scala SQL API, you can pass in new metadata when you alias a field.  That functionality is not available in the Python API.   Right now, you have to painfully utilize {{SparkSession.createDataFrame}} to manipulate the metadata for even a single column.  I would propose to add the following method to {{pyspark.sql.Column}}:
> {code}
> def aliasWithMetadata(self, name, metadata):
>     """
>     Make a new Column that has the provided alias and metadata.
>     Metadata will be processed with json.dumps()
>     """
>     _context = pyspark.SparkContext._active_spark_context
>     _metadata_str = json.dumps(metadata)
>     _metadata_jvm = _context._jvm.org.apache.spark.sql.types.Metadata.fromJson(_metadata_str)
>     _new_java_column = getattr(self._jc, 'as')(name, _metadata_jvm)
>     return Column(_new_java_column)
> {code}
> I can likely complete this request myself if there is any interest for it.  Just have to dust off my knowledge of doctest and the location of the python tests.



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