001/*
002 * Copyright (C) Photon Vision.
003 *
004 * This program is free software: you can redistribute it and/or modify
005 * it under the terms of the GNU General Public License as published by
006 * the Free Software Foundation, either version 3 of the License, or
007 * (at your option) any later version.
008 *
009 * This program is distributed in the hope that it will be useful,
010 * but WITHOUT ANY WARRANTY; without even the implied warranty of
011 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
012 * GNU General Public License for more details.
013 *
014 * You should have received a copy of the GNU General Public License
015 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
016 */
017
018package org.photonvision.common.util.numbers;
019
020import java.math.BigDecimal;
021import java.util.ArrayList;
022import java.util.Comparator;
023import java.util.List;
024import java.util.StringJoiner;
025
026@SuppressWarnings("unused")
027public class NumberListUtils {
028    /**
029     * @param collection an ArrayList of Comparable objects
030     * @return the median of collection
031     */
032    public static <T extends Number> double median(List<T> collection, Comparator<T> comp) {
033        double result;
034        int n = collection.size() / 2;
035
036        if (collection.size() % 2 == 0) // even number of items; find the middle two and average them
037        result =
038                    (nthSmallest(collection, n - 1, comp).doubleValue()
039                                    + nthSmallest(collection, n, comp).doubleValue())
040                            / 2.0;
041        else // odd number of items; return the one in the middle
042        result = nthSmallest(collection, n, comp).doubleValue();
043
044        return result;
045    }
046
047    public static <T extends Number> String toString(List<T> collection) {
048        return toString(collection, "");
049    }
050
051    public static <T extends Number> String toString(List<T> collection, String suffix) {
052        StringJoiner joiner = new StringJoiner(", ");
053        for (T x : collection) {
054            String s = x.doubleValue() + suffix;
055            joiner.add(s);
056        }
057        return joiner.toString();
058    }
059
060    /**
061     * @param collection an ArrayList of Numbers
062     * @return the mean of collection
063     */
064    public static double mean(final List<? extends Number> collection) {
065        BigDecimal sum = BigDecimal.ZERO;
066        for (final Number number : collection) {
067            sum = sum.add(BigDecimal.valueOf(number.doubleValue()));
068        }
069        return (sum.doubleValue() / collection.size());
070    }
071
072    /**
073     * @param collection a collection of Comparable objects
074     * @param n the position of the desired object, using the ordering defined on the collection
075     *     elements
076     * @return the nth smallest object
077     */
078    public static <T> T nthSmallest(List<T> collection, int n, Comparator<T> comp) {
079        T result, pivot;
080        ArrayList<T> underPivot = new ArrayList<>(),
081                overPivot = new ArrayList<>(),
082                equalPivot = new ArrayList<>();
083
084        // choosing a pivot is a whole topic in itself.
085        // this implementation uses the simple strategy of grabbing something from the middle of the
086        // ArrayList.
087
088        pivot = collection.get(n / 2);
089
090        // split collection into 3 lists based on comparison with the pivot
091
092        for (T obj : collection) {
093            int order = comp.compare(obj, pivot);
094
095            if (order < 0) // obj < pivot
096            underPivot.add(obj);
097            else if (order > 0) // obj > pivot
098            overPivot.add(obj);
099            else // obj = pivot
100            equalPivot.add(obj);
101        } // for each obj in collection
102
103        // recurse on the appropriate collection
104
105        if (n < underPivot.size()) result = nthSmallest(underPivot, n, comp);
106        else if (n < underPivot.size() + equalPivot.size()) // equal to pivot; just return it
107        result = pivot;
108        else // everything in underPivot and equalPivot is too small.  Adjust n accordingly in the
109            // recursion.
110            result = nthSmallest(overPivot, n - underPivot.size() - equalPivot.size(), comp);
111
112        return result;
113    }
114}