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From Peter Rudenko <petro.rude...@gmail.com>
Subject Re: what is metadata in StructField ?
Date Wed, 15 Jul 2015 10:37:41 GMT
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
>
>
>
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