| /* |
| * 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.math4.legacy.stat.descriptive.rank; |
| |
| import org.apache.commons.math4.legacy.core.MathArrays; |
| |
| /** |
| * Classic median of 3 strategy given begin and end indices. |
| * @since 3.4 |
| */ |
| public class MedianOf3PivotingStrategy implements PivotingStrategy { |
| /**{@inheritDoc} |
| * This in specific makes use of median of 3 pivoting. |
| * @return The index corresponding to a pivot chosen between the |
| * first, middle and the last indices of the array slice |
| * @throws org.apache.commons.math4.legacy.exception.MathIllegalArgumentException MathIllegalArgumentException when indices exceeds range |
| */ |
| @Override |
| public int pivotIndex(final double[] work, final int begin, final int end) { |
| MathArrays.verifyValues(work, begin, end - begin); |
| final int inclusiveEnd = end - 1; |
| final int middle = begin + (inclusiveEnd - begin) / 2; |
| final double wBegin = work[begin]; |
| final double wMiddle = work[middle]; |
| final double wEnd = work[inclusiveEnd]; |
| |
| if (wBegin < wMiddle) { |
| if (wMiddle < wEnd) { |
| return middle; |
| } else { |
| return wBegin < wEnd ? inclusiveEnd : begin; |
| } |
| } else { |
| if (wBegin < wEnd) { |
| return begin; |
| } else { |
| return wMiddle < wEnd ? inclusiveEnd : middle; |
| } |
| } |
| } |
| |
| } |