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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.statistics.ranking;
18  
19  import java.util.function.UnaryOperator;
20  
21  /**
22   * Interface representing a rank transformation.
23   *
24   * @since 1.1
25   */
26  @FunctionalInterface
27  public interface RankingAlgorithm extends UnaryOperator<double[]> {
28      /**
29       * <p>Performs a rank transformation on the input data, returning an array of
30       * ranks.
31       *
32       * <p>Ranks should be 1-based: the smallest value returned in an array of ranks
33       * should be greater than or equal to one, rather than 0. Ranks should in
34       * general take integer values, though implementations may return averages or
35       * other floating point values to resolve ties in the input data.
36       *
37       * @param data Array of data to be ranked.
38       * @return an array of ranks corresponding to the elements of the input array
39       */
40      @Override
41      double[] apply(double[] data);
42  }