Getting a null pointer while trying to write a model using ModelWriter

Legacy User

Hello,

I am trying to use rapidminer as a library. I'm trying something very simple to begin with. I read in a training data set, generate a model, and write the model out. I have been successful in doing this in the GUI, but it seems to fail when I try to do it progmatically. Here is my code:

public class Collect 
{
	public static void main(String[] args)
	{
		RapidMiner.init();
		try
		{
			Operator input = OperatorService.createOperator(ArffExampleSource.class);
			input.setParameter("data_file", "/home/vahid/Desktop/c_training.arff");
			input.setParameter("label_attribute", "change");

			IOContainer io = input.apply(new IOContainer());
			ExampleSet exampleSet = io.get(ExampleSet.class);

			Learner learner = (Learner) OperatorService.createOperator(NaiveBayes.class);
			Model model = learner.learn(exampleSet);

			ModelWriter writer = (ModelWriter) OperatorService.createOperator(ModelWriter.class);
			writer.setParameter("model_file", "/home/model.mod");
			writer.setParameter("overwrite_existing_file", "true");
			writer.setParameter("output_type", "XML");

			writer.apply();
		} 
		catch (OperatorCreationException e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (OperatorException e)
		{
			// TODO Auto-generated catch block
			e.printStackTrace();
		} 
	}
}

I tried to follow the manual when writing that code. Here is the error produced

Exception in thread "main" java.lang.NullPointerException
	at com.rapidminer.operator.Operator.getInput(Operator.java:821)
	at com.rapidminer.operator.Operator.getInput(Operator.java:802)
	at com.rapidminer.operator.io.ModelWriter.apply(ModelWriter.java:96)
	at Collect.main(Collect.java:33)

Any help is appreciated

steffen

Jumping by...

I think you forgot to tell the ModelWriter what to write out. Try this (not tested):

model.apply(new IOContainer(new IOObject[]{model}));

regards,

Steffen

Legacy User

Yes i thought about that. The problem is model is a Model object and Model.apply takes an ExampleSource as a parameter, not an IOContainer.  I think model.apply(ExampleSource) will be used when I load the model and want to aplly it to some data.

Thanks for the help though!

steffen

AAhhhhhhhhhh typo, me sorry

What I meant was:

writer.apply(new IOContainer(new IOObject[]{model}));

It is no good idea to think about this stuff so late in the evening. 

regards,

Steffen