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"Process failed: Exception: java.lang.NullPointerException in Aggregate"

Hi everyone! I'm new to RapidMiner (and data mining) so I hope you could help me.

I'm trying to get "Aggregate" to work but I get an error whenever I try to group by attributes. I get this error:

[tt]Exception: java.lang.NullPointerException
Message: null
Stack trace:

com.rapidminer.operator.preprocessing.transformation.aggregation.AggregationOperator$AggregationTreeNode.getChilds(AggregationOperator.java:108)
com.rapidminer.operator.preprocessing.transformation.aggregation.AggregationOperator.parseTree(AggregationOperator.java:394)
com.rapidminer.operator.preprocessing.transformation.aggregation.AggregationOperator.apply(AggregationOperator.java:324)
com.rapidminer.operator.AbstractExampleSetProcessing.doWork(AbstractExampleSetProcessing.java:116)
com.rapidminer.operator.Operator.execute(Operator.java:831)
com.rapidminer.operator.execution.SimpleUnitExecutor.execute(SimpleUnitExecutor.java:51)
com.rapidminer.operator.ExecutionUnit.execute(ExecutionUnit.java:709)
com.rapidminer.operator.OperatorChain.doWork(OperatorChain.java:369)
com.rapidminer.operator.Operator.execute(Operator.java:831)
com.rapidminer.Process.run(Process.java:902)
com.rapidminer.Process.run(Process.java:798)
com.rapidminer.Process.run(Process.java:793)
com.rapidminer.Process.run(Process.java:783)
com.rapidminer.gui.ProcessThread.run(ProcessThread.java:63)[/tt]

But when I remove all entries in "group by attributes" it works fine. Anyone know what I'm doing wrong?

Thanks!

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Accepted answers

All comments

Andrew2

Helllo

What is the type of the attribute you are grouping by? If it's a real, change it to a nominal.

Andrew

wessel

Hey,

This can be rather confusing indeed.
Lets say you have a real valued attribute with values: 0, 1, 2.
Surely you should be able to use this attribute to create groups, but you can't!

You need to first use the "Numerical to Polynominal" operator.
Then you can use the "Aggregate: operator.
And possibly you may have to use "Parse Numbers" to convert the attribute back to real.

This is rather cumbersome, but I think it is the only way.

Best regards,

Wessel

Mela

Thank you! They were integers. Changing them to polynominals worked.