[jira] [Created] (SPARK-22198) Java incompatibility when extending UnaryTransformer

["Akos Tomasits (JIRA)" <ji...@apache.org>]

Akos Tomasits created SPARK-22198:
-------------------------------------

             Summary: Java incompatibility when extending UnaryTransformer
                 Key: SPARK-22198
                 URL: https://issues.apache.org/jira/browse/SPARK-22198
             Project: Spark
          Issue Type: Bug
          Components: ML
    Affects Versions: 2.2.0
            Reporter: Akos Tomasits


It is not possible to create proper 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, this is not possible, 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() \{    	
          return sparkUid;
    }

    ...
{quote}




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