what is metadata in StructField ?

[matd <ma...@gmail.com>]

I see in StructField that we can provide metadata.

What is it meant for ?  How is it used by Spark later on ?
Are there any rules on what we can/cannot do with it ?

I'm building some DataFrame processing, and I need to maintain a set of
(meta)data along with the DF. I was wondering if I can use
StructField.metadata for this use, or if I should build my own structure.

Mathieu



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Re: what is metadata in StructField ?

[Peter Rudenko <pe...@gmail.com>]

Hi Mathieu,
metadata is very usefull if you need to save some data about a column 
(e.g. count of null values, cardinality, domain, min/max/std, etc.). 
It's currently used in ml package in attributes: 
https://github.com/apache/spark/blob/master/mllib/src/main/scala/org/apache/spark/ml/attribute/attributes.scala

Take a look how i'm using metadata to get summary statistics from h2o: 
https://github.com/h2oai/sparkling-water/pull/17/files

Let me know if you'll have questions.

Thanks,
Peter Rudenko

On 2015-07-15 12:48, matd wrote:
> I see in StructField that we can provide metadata.
>
> What is it meant for ?  How is it used by Spark later on ?
> Are there any rules on what we can/cannot do with it ?
>
> I'm building some DataFrame processing, and I need to maintain a set of
> (meta)data along with the DF. I was wondering if I can use
> StructField.metadata for this use, or if I should build my own structure.
>
> Mathieu
>
>
>
> --
> View this message in context: http://apache-spark-user-list.1001560.n3.nabble.com/what-is-metadata-in-StructField-tp23854.html
> Sent from the Apache Spark User List mailing list archive at Nabble.com.
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: user-unsubscribe@spark.apache.org
> For additional commands, e-mail: user-help@spark.apache.org
>


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