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https://issues.apache.org/jira/browse/SPARK-17161?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Bryan Cutler updated SPARK-17161:
---------------------------------
    Summary: Add PySpark-ML JavaWrapper convenience function to create py4j 
JavaArrays  (was: Add PySpark-ML JavaWrapper convienience function to create 
py4j JavaArrays)

> Add PySpark-ML JavaWrapper convenience function to create py4j JavaArrays
> -------------------------------------------------------------------------
>
>                 Key: SPARK-17161
>                 URL: https://issues.apache.org/jira/browse/SPARK-17161
>             Project: Spark
>          Issue Type: Improvement
>          Components: ML, PySpark
>            Reporter: Bryan Cutler
>            Priority: Minor
>
> Often in Spark ML, there are classes that use a Scala `Array` to construct.  
> In order to add the same API to Python, a Java-friendly alternate constructor 
> needs to exist to be compatible with py4j when converting from a list.  This 
> is because the current conversion in PySpark _py2java creates a 
> java.util.ArrayList, as shown in this error msg
> {noformat}
> Py4JError: An error occurred while calling 
> None.org.apache.spark.ml.feature.CountVectorizerModel. Trace:
> py4j.Py4JException: Constructor 
> org.apache.spark.ml.feature.CountVectorizerModel([class java.util.ArrayList]) 
> does not exist
>       at 
> py4j.reflection.ReflectionEngine.getConstructor(ReflectionEngine.java:179)
>       at 
> py4j.reflection.ReflectionEngine.getConstructor(ReflectionEngine.java:196)
>       at py4j.Gateway.invoke(Gateway.java:235)
> {noformat}
> Creating an alternate constructor can be avoided by creating a py4j JavaArray 
> using {{new_array}}.  This type is compatible with the Scala `Array` 
> currently used in classes like {{CountVectorizerModel}} and 
> {{StringIndexerModel}}.
> Most of the boiler-plate Python code to do this can be put in a convenience 
> function inside of  ml.JavaWrapper to give a clean way of constructing ML 
> objects without adding special constructors.



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