January 21, 2012

Will It Shuffle?

Or, why random comparators are bad (in addition to being slow).

This matrix diagram visualizes the probability of each element i being placed in position j at the end of a random shuffle. Red cells represent negative bias; green cells represent positive bias.

A good shuffling algorithm is unbiased; you should see a uniform grey matrix with only a bit of white noise. A bad algorithm will show streaks in the matrix, indicating an uneven distribution.

For more details, read my previous post on the Fisher–Yates shuffle. Also see screenshots of different browsers.

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January 21, 2012