What's the best way split users into random groups

Question

So here's my current problem is we are trying to implement a way to do AB testing. In my opinion the best way to separate users is probably by ID. Basically I would need to map their ID to a boolean (A or B/true or false).

The main problem I have with this though is I would want a method that can give different combinations for different AB testing scenarios. If I do something simple like convert to an Integer mod 2, it becomes difficult to use a parameter to create different groups (mathematically its difficult to make only some of the 1s go to 0 and vice versa even before the mod operation).

I think this leaves me with using a proper hashing algorithm like SHA1 but I figured I would ask if anyone else has a good way of doing this as well.

Answer 1

Maybe I'm missing something, but I'd start with:

Boolean b = Math.mod(Math.abs(u.Username.hashCode()), 2) == 0;

as user names have to be unique and don't change. And running something like this in the Developer Console to check that the distribution is as expected:

Boolean[] bs = new Boolean[] {};
for (User u : [select Username from User]) {
    Boolean b = Math.mod(Math.abs(u.Username.hashCode()), 2) == 0;
    bs.add(b);
}
System.debug('>>> ' + JSON.serialize(bs));

Answer 2

One simple way to do it I have used is to just assign a random number to each member in the list based on the list size e.g. User A : 4 User B : 1 User C : 3 User D : 2

Then assign based on even vs odd number.