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The Apache Commons Math project is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language or commons-lang.

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/*
 * 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.math3.stat.descriptive;

import org.apache.commons.math3.exception.MathIllegalArgumentException;

/**
 * Extends the definition of {@link UnivariateStatistic} with
 * {@link #increment} and {@link #incrementAll(double[])} methods for adding
 * values and updating internal state.
 * 
 * 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.
 *
 */
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 incrementally to the dataset.
     *
     * @param values  array holding the new values to add
     * @throws MathIllegalArgumentException if the array is null
     */
    void incrementAll(double[] values) throws MathIllegalArgumentException;

    /**
     * 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
     * incrementally 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 MathIllegalArgumentException if the array is null or the index
     */
    void incrementAll(double[] values, int start, int length) throws MathIllegalArgumentException;

    /**
     * Returns the current value of the Statistic.
     * @return value of the statistic, Double.NaN 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();

}