TouchDirWithFileDate/AggregateExtensions.cs at master · Sire/TouchDirWithFileDate · GitHub

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using NUnit.Framework;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;

namespace TouchDirWithFileDate
{
	static class AggregateExtensions
	{

        public static TSource Median<TSource>(this IEnumerable<TSource> source)
            where TSource : struct, INumber<TSource>
            => Median<TSource, TSource>(source);

        public static TResult Median<TSource, TResult>(this IEnumerable<TSource> source)
            where TSource : struct, INumber<TSource>
            where TResult : struct, INumber<TResult>
        {
            var array = source.ToArray();
            var length = array.Length;
            if (length == 0)
            {
                throw new InvalidOperationException("Sequence contains no elements.");
            }
            Array.Sort(array);
            var index = length / 2;
            var value = TResult.CreateChecked(array[index]);
            if (length % 2 == 1)
            {
                return value;
            }
            var sum = value + TResult.CreateChecked(array[index - 1]);
            return sum / TResult.CreateChecked(2);
        }

	}

    public class MedianTests
    {

        [Test]
        public void Median_PopulatedCollection_ReturnsCorrectResult()
        {
            // Arrange
            var source = new List<decimal> { 4.5m, 2.0m, 1.2m, 3.9m, 6.7m };
            var expected = 3.9m;

            // Act
            var actual = source.Median<decimal, decimal>();

            // Assert
            Assert.AreEqual(expected, actual);
        }

        [Test]
        public void Median_AverageIsUsedIfUnableToGetMedian()
        {
            // Arrange
            var source = new List<decimal> { 1m, 2m };
            var expected = source.Average(); //if median doesn't exist, use average

            // Act
            var actual = source.Median<decimal, decimal>();

            // Assert
            Assert.AreEqual(expected, actual);
        }

        [Test]
        public void Median_EmptyCollection_ThrowsInvalidOperationException()
        {
            // Arrange
            var source = new List<decimal>();

            // Act
            // Assert
            Assert.Throws<InvalidOperationException>(() => source.Median<decimal, decimal>());
        }

        [Test]
        public void Median_NullCollection_ThrowsArgumentNullException()
        {
            // Arrange
            List<decimal> source = null!;

            // Act
            // Assert
            Assert.Throws<System.ArgumentNullException>(() => source.Median<decimal, decimal>());
        }

        [Test]
        public void Median_CollectionWithOneValue_ReturnsCorrectResult()
        {
            // Arrange
            var source = new List<decimal> { 4.5m };
            var expected = 4.5m;

            // Act
            var actual = source.Median<decimal, decimal>();

            // Assert
            Assert.AreEqual(expected, actual);
        }
    }
}