Shuffling

Shuffling is the practice of reordering a set of items into a random or near-random sequence. It is used to reduce predictable order, increase fairness, and provide variety in activities such as card games, music playback, and data processing. The aim is to produce a permutation of the original items in which each possible order is equally likely, or as close to that as feasible.

Card shuffling: Physical methods include the riffle (or 'dovetail'), overhand, Hindu, and the precise but deterministic faro shuffle, which interleaves cards in a fixed pattern. In casual play, riffle and overhand shuffles are common. Studies in probability have shown that a standard 52-card deck becomes effectively random after several riffles; a result sometimes summarized as about seven such shuffles producing near-uniform distribution.

Algorithmic shuffling: In computing, shuffles are performed by algorithms such as the Fisher–Yates (Knuth) shuffle, which produces a uniformly random permutation in linear time using an in-place method. The algorithm repeatedly selects a random position and swaps elements, and it requires a source of true or pseudo-random numbers. Language libraries often provide a shuffle function built on this approach, with the randomness depending on the quality of the generator and seeding.

Randomness and biases: Real-world shuffles can introduce biases or correlations if performed carelessly. In digital contexts, the randomness source and seeding affect reproducibility and fairness. Shuffling is also used in simulations and randomized algorithms to ensure variability and exploration of sample space.