/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math.stat.descriptive;

/**
 * Extends the definition of {@link UnivariateStatistic} with {@link #increment}
 * and {@link #incrementAll(double[])} methods for adding values and updating
 * internal state.
 * <p>
 * This interface is designed to be used for calculating statistics that can be
 * computed in one pass through the data without storing the full array of
 * sample values.
 * </p>
 *
 * @version $Revision$ $Date$
 */
public interface StorelessUnivariateStatistic extends UnivariateStatistic {

	/**
	 * Updates the internal state of the statistic to reflect the addition of
	 * the new value.
	 * 
	 * @param d
	 *            the new value.
	 */
	void increment(double d);

	/**
	 * Updates the internal state of the statistic to reflect addition of all
	 * values in the values array. Does not clear the statistic first -- i.e.,
	 * the values are added <strong>incrementally</strong> to the dataset.
	 * 
	 * @param values
	 *            array holding the new values to add
	 * @throws IllegalArgumentException
	 *             if the array is null
	 */
	void incrementAll(double[] values);

	/**
	 * Updates the internal state of the statistic to reflect addition of the
	 * values in the designated portion of the values array. Does not clear the
	 * statistic first -- i.e., the values are added
	 * <strong>incrementally</strong> to the dataset.
	 * 
	 * @param values
	 *            array holding the new values to add
	 * @param start
	 *            the array index of the first value to add
	 * @param length
	 *            the number of elements to add
	 * @throws IllegalArgumentException
	 *             if the array is null or the index
	 */
	void incrementAll(double[] values, int start, int length);

	/**
	 * Returns the current value of the Statistic.
	 * 
	 * @return value of the statistic, <code>Double.NaN</code> if it has been
	 *         cleared or just instantiated.
	 */
	double getResult();

	/**
	 * Returns the number of values that have been added.
	 * 
	 * @return the number of values.
	 */
	long getN();

	/**
	 * Clears the internal state of the Statistic
	 */
	void clear();

	/**
	 * Returns a copy of the statistic with the same internal state.
	 * 
	 * @return a copy of the statistic
	 */
	StorelessUnivariateStatistic copy();

}