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A Java's Collaborative Filtering library to carry out experiments in research of Collaborative Filtering based Recommender Systems. The library has been designed from researchers to researchers.

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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;
import org.apache.commons.math3.util.MathArrays;


/**
 * Base interface implemented by all statistics.
 *
 */
public interface UnivariateStatistic extends MathArrays.Function {
    /**
     * Returns the result of evaluating the statistic over the input array.
     *
     * @param values input array
     * @return the value of the statistic applied to the input array
     * @throws MathIllegalArgumentException  if values is null
     */
    double evaluate(double[] values) throws MathIllegalArgumentException;

    /**
     * Returns the result of evaluating the statistic over the specified entries
     * in the input array.
     *
     * @param values the input array
     * @param begin the index of the first element to include
     * @param length the number of elements to include
     * @return the value of the statistic applied to the included array entries
     * @throws MathIllegalArgumentException if values is null or the indices are invalid
     */
    double evaluate(double[] values, int begin, int length) throws MathIllegalArgumentException;

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