source: branches/2825-NSGA3/HeuristicLab.Algorithms.NSGA3/3.3/Utility.cs @ 17616

using System;
using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Data;

namespace HeuristicLab.Algorithms.NSGA3
{
    internal static class Utility
    {
        internal static List<T> Concat<T>(List<T> list1, List<T> list2)
        {
            List<T> resultList = new List<T>(list1.Count + list2.Count);

            resultList.AddRange(list1);
            resultList.AddRange(list2);

            return resultList;
        }

        /// <summary>
        /// Returns the number of possible combinations of size <paramref name="r" /> from a set of
        /// size <paramref name="n" />.
        /// </summary>
        /// <param name="n"></param>
        /// <param name="r"></param>
        /// <returns></returns>
        /// <exception cref="ArgumentException">
        /// Thrown, when <paramref name="r" /> &gt; <paramref name="n" /> or when <paramref name="r"
        /// /> &lt; 1.
        /// </exception>
        internal static int NCR(int n, int r)
        {
            if (n < r) throw new ArgumentException($"Constraint was not met: n >= r (n = {n}, r = {r})");
            if (r < 1) throw new ArgumentException($"Constraint was not met: r >= 1 (r = {r})");
            if (n == r) return n;
            return Factorial(n) / (Factorial(r) * Factorial(n - r));
        }

        internal static int Factorial(int n)
        {
            if (n <= 0) throw new ArgumentException($"Constraint for n was not met: 0 < n <= 30 (n = {n})");
            int product = 1;
            for (int i = 2; i <= n; i++)
                product *= i;

            return product;
        }

        internal static DoubleMatrix ConvertToDoubleMatrix(List<ReferencePoint> referencePoints)
        {
            return new DoubleMatrix(ToArray(referencePoints));
        }

        internal static double[][] ToFitnessMatrix(this List<Solution> solutions)
        {
            double[][] data = new double[solutions.Count][];
            for (int i = 0; i < solutions.Count; i++)
            {
                Solution solution = solutions[i];
                data[i] = new double[solution.Fitness.Length];
                for (int j = 0; j < solution.Fitness.Length; j++)
                {
                    data[i][j] = solution.Fitness[j];
                }
            }

            return data;
        }

        internal static DoubleMatrix ToMatrix(this IEnumerable<IReadOnlyList<double>> data)
        {
            var d2 = data.ToArray();
            var mat = new DoubleMatrix(d2.Length, d2[0].Count);
            for (var i = 0; i < mat.Rows; i++)
                for (var j = 0; j < mat.Columns; j++)
                    mat[i, j] = d2[i][j];
            return mat;
        }

        private static double[,] ToArray(List<ReferencePoint> referencePoints)
        {
            if (referencePoints == null || !referencePoints.Any()) throw new ArgumentException($"{nameof(referencePoints)} is null or empty");
            int nDim = referencePoints.First().NumberOfDimensions;
            int pointCount = referencePoints.Count;
            double[,] array = new double[nDim, pointCount];

            for (int p = 0; p < pointCount; p++)
                for (int d = 0; d < nDim; d++)
                    array[d, p] = referencePoints[p].Values[d];

            return array;
        }

        internal static TOut Min<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            //var it = inputs.GetEnumerator();
            //it.MoveNext();
            //var minValue = func(it.Current);
            //while (it.MoveNext())
            //{
            //    var currentValue = func(it.Current);
            //    if (minValue.CompareTo(currentValue) > 0) minValue = currentValue;
            //}

            //return minValue;
            return MinArgMin(func, inputs).Item2;
        }

        internal static TIn ArgMin<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MinArgMin(func, inputs).Item1;
        }

        internal static Tuple<TIn, TOut> MinArgMin<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            var it = inputs.GetEnumerator();
            it.MoveNext();
            var minArg = it.Current;
            var minValue = func(it.Current);
            while (it.MoveNext())
            {
                var currentArg = it.Current;
                var currentValue = func(it.Current);
                if (minValue.CompareTo(currentValue) > 0)
                {
                    minArg = currentArg;
                    minValue = currentValue;
                }
            }

            return Tuple.Create(minArg, minValue);
        }

        internal static TOut Max<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            //var it = inputs.GetEnumerator();
            //it.MoveNext();
            //var maxValue = func(it.Current);
            //while (it.MoveNext())
            //{
            //    var currentValue = func(it.Current);
            //    if (maxValue.CompareTo(currentValue) < 0) maxValue = currentValue;
            //}

            //return maxValue;
            return MaxArgMax(func, inputs).Item2;
        }

        internal static TIn ArgMax<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            return MaxArgMax(func, inputs).Item1;
        }

        internal static Tuple<TIn, TOut> MaxArgMax<TIn, TOut>(Func<TIn, TOut> func, IEnumerable<TIn> inputs) where TOut : IComparable
        {
            var it = inputs.GetEnumerator();
            it.MoveNext();
            var maxArg = it.Current;
            var maxValue = func(it.Current);
            while (it.MoveNext())
            {
                var currentArg = it.Current;
                var currentValue = func(it.Current);
                if (maxValue.CompareTo(currentValue) < 0)
                {
                    maxArg = currentArg;
                    maxValue = currentValue;
                }
            }

            return Tuple.Create(maxArg, maxValue);
        }
    }
}