"Weighted random" object picker (based on http://www.perlmonks.org/?node_id=242751)

1-WeightedObjectPickerExample.cs

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    // Demo
    static void Main(string[] args)
    {
        // Define some weighted object (in this case: strings, but could be anything (e.g. "Customer") and set their weights
        var myobjects = new[]
        {
            new WeightedObject<string>("A", 2),
            new WeightedObject<string>("B", 3),
            new WeightedObject<string>("C", 5),
            new WeightedObject<string>("D", 10)
        };

        // For <iterations> iterations pick a random object from the above array; keep track of the results in a list
        var iterations = 10000;
        var results = new List<WeightedObject<string>>();
        for (int i = 0; i < iterations; i++)
            results.Add(WeightedObjectPicker.PickWeightedObject(myobjects));

        // Print the number of times each object was picked and also present this as a percentage
        Console.WriteLine(
            string.Join("\r\n", results.GroupBy(o => o.Object).OrderBy(g => g.Key).Select(g => $"{g.Key}\t{g.Count()}\t{(double)g.Count() / iterations:P2}%"))
        );
    }
}

// Picks 'weighted random' objects from an array of objects
public class WeightedObjectPicker
{
    // Initialize RNG
    private static readonly Random rng = new Random();

    public static WeightedObject<T> PickWeightedObject<T>(WeightedObject<T>[] objects)
    {
        // Initialize indexer to point to first object in array, get total weight of objects, pick random number below total weight
        int i = 0, totalweight = objects.Sum(o => o.Weight), r = rng.Next(totalweight);
        // Note: we may want to check totalweight to be greater than 0
        // While the random number >= 0
        while (r >= 0)
            r -= objects[i++].Weight;   // Subtract indexed object's weight, increase indexer
        // Decrease indexer by one (we incremented it one time too many) and return indexed object
        return objects[--i];
    }
}

// Represents a weighted object of type T
public class WeightedObject<T>
{
    // The object's weight
    public int Weight { get; private set; }
    // The object
    public T Object { get; private set; }

    // Initialize new weighted object of T with it's weight
    public WeightedObject(T obj, int weight)
    {
        if (weight < 0)
            throw new ArgumentOutOfRangeException("Weight must be >= 0");

        this.Object = obj;
        this.Weight = weight;
    }
}

2-exampleoutput.cmd

A       1023    10,23 %%
B       1530    15,30 %%
C       2497    24,97 %%
D       4950    49,50 %%