selection based on percentage weighting

Question

I have a set of values, and an associated percentage for each:

a: 70% chance
b: 20% chance
c: 10% chance

I want to select a value (a, b, c) based

Answer 1

I've my own solution for this:

public class Randomizator3000 
{    
public class Item
{
    public T value;
    public float weight;

    public static float GetTotalWeight(Item[] p_itens)
    {
        float __toReturn = 0;
        foreach(var item in p_itens)
        {
            __toReturn += item.weight;
        }

        return __toReturn;
    }
}

private static System.Random _randHolder;
private static System.Random _random
{
    get 
    {
        if(_randHolder == null)
            _randHolder = new System.Random();

        return _randHolder;
    }
}

public static T PickOne(Item[] p_itens)
{   
    if(p_itens == null || p_itens.Length == 0)
    {
        return default(T);
    }

    float __randomizedValue = (float)_random.NextDouble() * (Item.GetTotalWeight(p_itens));
    float __adding = 0;
    for(int i = 0; i < p_itens.Length; i ++)
    {
        float __cacheValue = p_itens[i].weight + __adding;
        if(__randomizedValue <= __cacheValue)
        {
            return p_itens[i].value;
        }

        __adding = __cacheValue;
    }

    return p_itens[p_itens.Length - 1].value;

}
}

And using it should be something like that (thats in Unity3d)

using UnityEngine;
using System.Collections;

public class teste : MonoBehaviour 
{
Randomizator3000.Item[] lista;

void Start()
{
    lista = new Randomizator3000.Item[10];
    lista[0] = new Randomizator3000.Item();
    lista[0].weight = 10;
    lista[0].value = "a";

    lista[1] = new Randomizator3000.Item();
    lista[1].weight = 10;
    lista[1].value = "b";

    lista[2] = new Randomizator3000.Item();
    lista[2].weight = 10;
    lista[2].value = "c";

    lista[3] = new Randomizator3000.Item();
    lista[3].weight = 10;
    lista[3].value = "d";

    lista[4] = new Randomizator3000.Item();
    lista[4].weight = 10;
    lista[4].value = "e";

    lista[5] = new Randomizator3000.Item();
    lista[5].weight = 10;
    lista[5].value = "f";

    lista[6] = new Randomizator3000.Item();
    lista[6].weight = 10;
    lista[6].value = "g";

    lista[7] = new Randomizator3000.Item();
    lista[7].weight = 10;
    lista[7].value = "h";

    lista[8] = new Randomizator3000.Item();
    lista[8].weight = 10;
    lista[8].value = "i";

    lista[9] = new Randomizator3000.Item();
    lista[9].weight = 10;
    lista[9].value = "j";
}


void Update () 
{
    Debug.Log(Randomizator3000.PickOne(lista));
}
}

In this example each value has a 10% chance do be displayed as a debug =3