How to make a randomizer which excludes already fallen numbers?

How to make a randomizer which excludes already fallen numbers?

Not sure that this is the most efficient way of doing it, but here’s what I came up with real quick:

It stores a random integer determined by how many options there are in a given array, then uses that same integer to find the corresponding item within that array, then immediately removes the item from the array so it can’t be chosen again.