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https://issues.apache.org/jira/browse/SPARK-22198?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Akos Tomasits updated SPARK-22198:
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Summary: Java incompatibility when extending UnaryTransformer or
Transformer (was: Java incompatibility when extending UnaryTransformer)
> Java incompatibility when extending UnaryTransformer or Transformer
> -------------------------------------------------------------------
>
> Key: SPARK-22198
> URL: https://issues.apache.org/jira/browse/SPARK-22198
> Project: Spark
> Issue Type: Bug
> Components: Java API, ML
> Affects Versions: 2.2.0
> Reporter: Akos Tomasits
> Priority: Major
>
> It is not possible to create proper Java custom Transformer by extending
> UnaryTransformer.
> It seems that the method 'uid()' is called during object creation before the
> provided 'uid' constructor parameter could be set.
> This leads to the following error:
> {quote}
> java.lang.IllegalArgumentException: requirement failed: Param
> <prefix>_1563950936fa__inputCol does not belong to <prefix>_d4105b75c4aa.
> {quote}
> If you extend UnaryTransformer and try to use it e.g. through CrossValidator,
> you will need to explicitly include a constructor, which receives a String
> parameter. As I saw in the source of built in transformers, this parameter is
> a 'uid', which should be set in the object. However, it is not possible to do
> it in time, because the uid() method is invoked (and its result might be
> used) before this constructor finishes.
> Sample class:
> {quote}
> public class TextCleaner extends UnaryTransformer<String, String, TextCleaner>
> implements Serializable, DefaultParamsWritable,
> DefaultParamsReadable<TextCleaner> \{
> private static final long serialVersionUID = 2658543236303100458L;
>
> private static final String sparkUidPrefix = "TextCleaner";
>
> private final String sparkUid;
> public TextCleaner() \{
> sparkUid =
> org.apache.spark.ml.util.Identifiable$.MODULE$.randomUID(sparkUidPrefix);
> }
> public TextCleaner(String uid) \{
> sparkUid = uid;
> }
>
> @Override
> public String uid() \{ // This method is called by parent class, before
> object creation finishes
> return sparkUid;
> }
> ...
> {quote}
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