/*
 * 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();

}