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https://issues.apache.org/jira/browse/SPARK-17025?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16101994#comment-16101994
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Weichen Xu commented on SPARK-17025:
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Because currently, scala calling python will be difficult and changing related
code is hard, Maybe we can consider the way that we duplicate the import/export
logic by python implementation, adding a python implemented MLWriter for
pyspark.ml.PipelineModel, it traverse the list of model, if a model is
"javaModel" than call the java-side writer, otherwise just call itself python
implemented writer.
> Cannot persist PySpark ML Pipeline model that includes custom Transformer
> -------------------------------------------------------------------------
>
> Key: SPARK-17025
> URL: https://issues.apache.org/jira/browse/SPARK-17025
> Project: Spark
> Issue Type: New Feature
> Components: ML, PySpark
> Affects Versions: 2.0.0
> Reporter: Nicholas Chammas
> Priority: Minor
>
> Following the example in [this Databricks blog
> post|https://databricks.com/blog/2016/05/31/apache-spark-2-0-preview-machine-learning-model-persistence.html]
> under "Python tuning", I'm trying to save an ML Pipeline model.
> This pipeline, however, includes a custom transformer. When I try to save the
> model, the operation fails because the custom transformer doesn't have a
> {{_to_java}} attribute.
> {code}
> Traceback (most recent call last):
> File ".../file.py", line 56, in <module>
> model.bestModel.save('model')
> File
> "/usr/local/Cellar/apache-spark/2.0.0/libexec/python/lib/pyspark.zip/pyspark/ml/pipeline.py",
> line 222, in save
> File
> "/usr/local/Cellar/apache-spark/2.0.0/libexec/python/lib/pyspark.zip/pyspark/ml/pipeline.py",
> line 217, in write
> File
> "/usr/local/Cellar/apache-spark/2.0.0/libexec/python/lib/pyspark.zip/pyspark/ml/util.py",
> line 93, in __init__
> File
> "/usr/local/Cellar/apache-spark/2.0.0/libexec/python/lib/pyspark.zip/pyspark/ml/pipeline.py",
> line 254, in _to_java
> AttributeError: 'PeoplePairFeaturizer' object has no attribute '_to_java'
> {code}
> Looking at the source code for
> [ml/base.py|https://github.com/apache/spark/blob/acaf2a81ad5238fd1bc81e7be2c328f40c07e755/python/pyspark/ml/base.py],
> I see that not even the base Transformer class has such an attribute.
> I'm assuming this is missing functionality that is intended to be patched up
> (i.e. [like
> this|https://github.com/apache/spark/blob/acaf2a81ad5238fd1bc81e7be2c328f40c07e755/python/pyspark/ml/classification.py#L1421-L1433]).
> I'm not sure if there is an existing JIRA for this (my searches didn't turn
> up clear results).
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