When random is not actually random enough
This article explains the technical flaw in using the modulo operator to select items from a set using a random number generator. It demonstrates how this method creates a non-uniform distribution, leading to biased selection results.
Why it matters
It addresses a common programming pitfall that can lead to subtle, hard-to-debug logic errors in software systems requiring true randomness.
There is a common pattern you see pop up in codebases everywhere that many of us have written: given a set of objects, pick one at random. Every object should have the same chance of being picked. A rather simple and direct solution is to pick a big random number, then clamp that number to the number of choices by modulo:
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