/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2011 by Rapid-I and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapid-i.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see http://www.gnu.org/licenses/.
 */
package com.rapidminer.operator.preprocessing;

import java.util.List;

import com.rapidminer.example.Attribute;
import com.rapidminer.example.ExampleSet;
import com.rapidminer.example.set.SplittedExampleSet;
import com.rapidminer.operator.Operator;
import com.rapidminer.operator.OperatorDescription;
import com.rapidminer.operator.OperatorException;
import com.rapidminer.operator.UserError;
import com.rapidminer.operator.ports.InputPort;
import com.rapidminer.operator.ports.OutputPort;
import com.rapidminer.operator.ports.metadata.AttributeSetPrecondition;
import com.rapidminer.parameter.ParameterType;
import com.rapidminer.parameter.ParameterTypeAttribute;
import com.rapidminer.tools.Ontology;


/**
 * <p>This operator creates a SplittedExampleSet from an arbitrary example set. 
 * The partitions of the resulting example set are created according to the 
 * values of the specified attribute. This works similar to the 
 * <code>GROUP BY</code> clause in SQL.</p>
 * 
 * <p>Please note that the resulting example set is simply a splitted example
 * set where no subset is selected. Following operators might decide to select
 * one or several of the subsets, e.g. one of the aggregation operators.</p>
 * 
 * @author Christian Bockermann, Ingo Mierswa
 */
public class GroupByOperator extends Operator {

	public final static String PARAMETER_ATTRIBUTE_NAME = "attribute_name";

	private InputPort exampleSetInput = getInputPorts().createPort("example set");
	private OutputPort exampleSetOutput = getOutputPorts().createPort("example set");

	public GroupByOperator(OperatorDescription desc) {
		super(desc);

		exampleSetInput.addPrecondition(new AttributeSetPrecondition(exampleSetInput, AttributeSetPrecondition.getAttributesByParameter(this, PARAMETER_ATTRIBUTE_NAME), Ontology.NOMINAL));
		getTransformer().addPassThroughRule(exampleSetInput, exampleSetOutput);
	}

	@Override
	public void doWork() throws OperatorException {
		ExampleSet exampleSet = exampleSetInput.getData();
		Attribute attribute = exampleSet.getAttributes().get(this.getParameterAsString(PARAMETER_ATTRIBUTE_NAME));

		if (attribute == null) {
			throw new UserError(this, 111, this.getParameterAsString(PARAMETER_ATTRIBUTE_NAME));
		}

		if (!attribute.isNominal()) {
			throw new UserError(this, 103, new Object[] { this.getParameterAsString(PARAMETER_ATTRIBUTE_NAME), "grouping by attribute." });
		}

		SplittedExampleSet grouped = SplittedExampleSet.splitByAttribute(exampleSet, attribute);

		exampleSetOutput.deliver(grouped);
	}

	@Override
	public List<ParameterType> getParameterTypes() {
		List<ParameterType> types = super.getParameterTypes();
		types.add(new ParameterTypeAttribute(PARAMETER_ATTRIBUTE_NAME, "Name of the nominal attribute which is used to create partitions.", exampleSetInput, false, Ontology.NOMINAL));
		return types;
	}
}