001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.statistics.ranking;
018
019import java.util.function.UnaryOperator;
020
021/**
022 * Interface representing a rank transformation.
023 *
024 * @since 1.1
025 */
026@FunctionalInterface
027public interface RankingAlgorithm extends UnaryOperator<double[]> {
028    /**
029     * <p>Performs a rank transformation on the input data, returning an array of
030     * ranks.
031     *
032     * <p>Ranks should be 1-based: the smallest value returned in an array of ranks
033     * should be greater than or equal to one, rather than 0. Ranks should in
034     * general take integer values, though implementations may return averages or
035     * other floating point values to resolve ties in the input data.
036     *
037     * @param data Array of data to be ranked.
038     * @return an array of ranks corresponding to the elements of the input array
039     */
040    @Override
041    double[] apply(double[] data);
042}