private static AttributeSelection getAttributeSelector(
		Instances trainingData) throws Exception {
	AttributeSelection selector = new AttributeSelection();
	InfoGainAttributeEval evaluator = new InfoGainAttributeEval();
	Ranker ranker = new Ranker();
	ranker.setNumToSelect(Math.min(500, trainingData.numAttributes() - 1));
	selector.setEvaluator(evaluator);
	selector.setSearch(ranker);
	selector.SelectAttributes(trainingData);
	return selector;
}
 

public static Instances preProcessData(Instances data) throws Exception{
	
	/* 
	 * Remove useless attributes
	 */
	RemoveUseless removeUseless = new RemoveUseless();
	removeUseless.setOptions(new String[] { "-M", "99" });	// threshold
	removeUseless.setInputFormat(data);
	data = Filter.useFilter(data, removeUseless);

	
	/* 
	 * Remove useless attributes
	 */
	ReplaceMissingValues fixMissing = new ReplaceMissingValues();
	fixMissing.setInputFormat(data);
	data = Filter.useFilter(data, fixMissing);
	

	/* 
	 * Remove useless attributes
	 */
	Discretize discretizeNumeric = new Discretize();
	discretizeNumeric.setOptions(new String[] {
			"-O",
			"-M",  "-1.0", 
			"-B",  "4",  // no of bins
			"-R",  "first-last"}); //range of attributes
	fixMissing.setInputFormat(data);
	data = Filter.useFilter(data, fixMissing);

	/* 
	 * Select only informative attributes
	 */
	InfoGainAttributeEval eval = new InfoGainAttributeEval();
	Ranker search = new Ranker();
	search.setOptions(new String[] { "-T", "0.001" });	// information gain threshold
	AttributeSelection attSelect = new AttributeSelection();
	attSelect.setEvaluator(eval);
	attSelect.setSearch(search);
	
	// apply attribute selection
	attSelect.SelectAttributes(data);
	
	// remove the attributes not selected in the last run
	data = attSelect.reduceDimensionality(data);
	
	

	return data;
}