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.descriptive;
18
19 /**
20 * Defines a transformer for {@code NaN} values in arrays.
21 *
22 * <p>This interface is not intended for a public API. It provides a consistent method
23 * to handle partial sorting of {@code double[]} data in the {@link Median} and
24 * {@link Quantile} classes.
25 *
26 * <p>The transformer allows pre-processing floating-point data before applying a sort algorithm.
27 * This is required to handle {@code NaN}.
28 *
29 * <p>Note: The {@code <} relation does not provide a total order on all double
30 * values: {@code -0.0 == 0.0} is {@code true} and a {@code NaN}
31 * value compares neither less than, greater than, nor equal to any value,
32 * even itself.
33 *
34 * <p>The {@link Double#compare(double, double)} method imposes the ordering:
35 * {@code -0.0} is treated as less than value
36 * {@code 0.0} and {@code Double.NaN} is considered greater than any
37 * other value and all {@code Double.NaN} values are considered equal.
38 *
39 * <p>This interface allows implementations to respect the behaviour of
40 * {@link Double#compare(double, double)}, or implement different behaviour.
41 *
42 * @since 1.1
43 */
44 interface NaNTransformer {
45 /**
46 * Pre-process the data for partitioning.
47 *
48 * <p>This method will scan all the data and apply processing to {@code NaN} values.
49 *
50 * <p>The method will return:
51 * <ul>
52 * <li>An array to partition; this may be a copy.
53 * <li>The {@code size} of the data; this can be smaller than the input array length if
54 * the transformer is configured to exclude NaN values.
55 * </ul>
56 *
57 * @param data Data.
58 * @param bounds [size].
59 * @return pre-processed data (may be a copy)
60 */
61 double[] apply(double[] data, int[] bounds);
62 }