chooseWithChance.cs - Choose a random member of a set with a given chance of selection.

chooseWithChance.cs

public static Random random = new Random(DateTime.Now.Millisecond);
public int chooseWithChance(params int[] args)
        {
            /*
             * This method takes number of chances and randomly chooses
             * one of them considering their chance to be choosen.    
             * e.g. 
             *   chooseWithChance(1,99) will most probably (%99) return 1 since index of 99 is 1
             *   chooseWithChance(99,1) will most probably (%99) return 0 since index of 99 is 0     
             *   chooseWithChance(0,100) will always return 1.
             *   chooseWithChance(10,10,80) will most probably (%80) return 2 since index of 80 is 2
             */
            int argCount = args.Length;
            int sumOfChances = 0;
        
            for (int i = 0; i < argCount; i++) {
                sumOfChances += args[i];
            }
        
            double randomDouble = random.NextDouble() * sumOfChances;
                    
            while (sumOfChances > randomDouble)
            {
                sumOfChances -= args[argCount -1];
                argCount--;
            }
        
            return argCount-1;
        }

Awesome!