Weighted random

using System;

using System.Linq;

using System.Collections.Generic;

public class WeightedItem<T>

{

public T Item { get; set; }

public double Weight { get; set; } = 1;

}

class WeightedRandom<T>

{

private static Random random = new Random();

private List<WeightedItem<T>> list { get; set; } = new List<WeightedItem<T>>();

public WeightedItem<T> this[T item] => list.FirstOrDefault(x => x.Item.Equals(item)) ?? ((Func<WeightedItem<T>>)(() => { list.Add(new WeightedItem<T>{ Item = item }); return this[item]; }))();

public double TotalWeight => list.Sum(x => x.Weight);

public WeightedRandom(params T[] items) => list.AddRange(items.Select(x => new WeightedItem<T> { Item = x }));

public WeightedRandom(IEnumerable<T> items):this(items.ToArray()) {}

public T Next()

{

var limit = list.Sum(x => x.Weight);

var value = random.NextDouble() * limit;

var e = list.GetEnumerator();

while(e.MoveNext())

if((e.Current.Weight) > value)

return e.Current.Item;

else

value -= e.Current.Weight;

return e.Current.Item;

}

}

class MainClass

{

static void Main()

{

var items = new[] { "Sam", "Lia", "Kind Lenny", "Boomer Badlad", "Handsum Jim" };

var occurs = new Dictionary<string, int>();

var rand = new WeightedRandom<string>(items);

rand["Sam"].Weight = 5;

rand["Handsum Jim"].Weight = .5;

var length = rand.TotalWeight * 1000000;

for(var i = 0; i < length; i++)

{

var item = rand.Next();

if(occurs.ContainsKey(item))

occurs[item]++;

else

occurs[item] = 1;

}

foreach(var item in items)

Console.WriteLine($"{item}: {occurs[item]}");

}

}