Influenced randomization

Question

I'm really sorry, I would search my question but I don't know how to word it correctly, I have a big problem with mental math and I've been trying to think of a solution. I'm trying to build a program for my guild that will add names to a list. This list has a parallel struct for each entry that holds the person's name and number of donations to a raffle.

I want to randomize through all the names and have the results positively influenced by the amount of donations people have put in. likes 1 or 1% increase in possibility * number of donations. I've done randomization before but I've never had to influence the odds slightly. help me please? I would post code but I don't have ANY randomization at the time. I can give you some other stuff though:

I made a struct to hold each user's entry:

    public struct pEntry
    {
        public string Name;
        public int Entries;
    }

I made a list to hold all the entries:

    public List<pEntry> lEntries = new List<pEntry>();

I want my randomization to be positively influenced by the number of entries(donations) they've made. This has no cap on how high it can go but if I need to maybe I can make it like.. 255.After it randomizes it will pick display a message saying that, that user has won and it will remove that entry from the list and pick a few more. This program will be used for multiple raffles and things like it but all use the same system.

Why not just have a list of strings; anyone who buys two tickets gets put on the list twice. If they buy three tickets, they get put on the list three times. Then just choose a random item from the list. After all, that's how it actually works with real paper tickets. — Eric Lippert, Apr 27 '13 at 00:40
If you need something quick and dirty, you could fill add an entrant to a temp array for every entry they made. Then you could randomize the index for that collection. EDIT: @EricLippert beat me to it =) — TyCobb, Apr 27 '13 at 00:40
Note also that if there is serious money on the line here then you should use a *cryptographically secure source of randomness*. The "random" numbers generated by Math.Random actually highly predictable; they are only pseudo-random. — Eric Lippert, Apr 27 '13 at 00:44
Haha, you guys are great. Yea, I guess I was overcomplicating it, I'll try a unique UID as to avoid duplication. Thank you, I really appreciate it :) — Tsproggy, Apr 27 '13 at 00:50
The way the question is phrased sounds like everyone gets a base "chance" of winning (ie, a free ticket), and he wants to generate bonus chances based on size of donations but not have it so that someone that donates 10 units gets 11 chances (ie, 1 free ticket and 10 bonus tickets). But he will need to decide exactly how big a donation increases the chances to work out the math he needs. — StarPilot, Apr 27 '13 at 00:52
If you need or prefer a "real" weighted approach, see http://stackoverflow.com/questions/56692/random-weighted-choice — Tim S., Apr 27 '13 at 00:54

StarPilot · Accepted Answer · 2013-04-30T17:47:54.067

You need to know how much donations increase the chance of winning. Does 1 = 1 more chance than someone that hasn't donated? Once you have a base and a bonus, you can just generate a "chart", see what your top number is, and generate a random number. After that, you can remove that person or reset their chances by whatever fraction you want, regenerate your chance list, and generate a new number.

For instance, if you want 1 donation unit to give 10% more chance for that person, then you could generate a list of all the guild, and each person gets 10 "lots" + 1 lot per donation unit. So if you had 3 people, where:

Ann gave 5 donation units
Tom gave 2 donation units
Bob didn't give any

The resulting list would be:

Ann lot count: 10 (base) + 5 (donations) = 15 lots
Tom lot count: 10 (base) + 2 (donations) = 12 lots
Bob lot count: 10 (base) + 0 (no donations) = 10 lots

Then you generate a number between 1 and 37 (15 + 12 + 10) to determine the winner.

Figure out what each donation should improve their odds (increases in their lots) and then you can start building your ranges and generate your numbers.

Influenced randomization

1 Answers1