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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2016/06/02 14:20:59 UTC
[jira] [Commented] (SPARK-15642) Metadata gets lost when selecting
a field of a StructType
[ https://issues.apache.org/jira/browse/SPARK-15642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15312379#comment-15312379 ]
Apache Spark commented on SPARK-15642:
--------------------------------------
User 'zommerfelds' has created a pull request for this issue:
https://github.com/apache/spark/pull/13467
> Metadata gets lost when selecting a field of a StructType
> ---------------------------------------------------------
>
> Key: SPARK-15642
> URL: https://issues.apache.org/jira/browse/SPARK-15642
> Project: Spark
> Issue Type: Bug
> Components: PySpark
> Affects Versions: 1.6.0, 1.6.1
> Reporter: Christian Zommerfelds
>
> Hi,
> When working with Data Frames, sometimes I find myself needing to write a function that creates multiple columns. Since that is not directly possible, I create a function that returns a StructType, and then call select() to assign the fields to different columns. However, I noticed that the metadata gets lost when I do that.
> Example:
> {code}
> In: schema = StructType([StructField('foo', StructType([
> StructField('features', ArrayType(IntegerType())),
> StructField('label', DoubleType(), False,
> {'ml_attr': {'type': 'nominal', 'vals': ['0.0', '1.0']}}
> )
> ]))])
> In: df = sqlContext.createDataFrame([Row(foo=Row(features=[1,2], label=0.0)), Row(foo=Row(features=[3,4], label=1.0))], schema)
> In: df.schema.fields[0].dataType.fields[1].metadata
> Out: {'ml_attr': {'type': 'nominal', 'vals': ['0.0', '1.0']}}
> In: df2 = df.select(df.foo['label'])
> In: df2.schema.fields[0].metadata
> Out: {}
> {code}
> Expected: same metadata (ml_attrib...)
> My work around is to create a new Data Frame from RDD, because as far as I know PySpark doesn't support adding metadata once the DF is created (should I create another issue for that?). Work around example:
> {code}
> In: df3 = sqlContext.createDataFrame(df2.rdd, StructType([schema.fields[0].dataType.fields[1]]))
> In: df3.schema.fields[0].metadata
> Out: {'ml_attr': {'type': 'nominal', 'vals': ['0.0', '1.0']}}
> {code}
> I am not sure if this affects the Scala API.
> Let me know if I can provide any other information.
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