Pseudo Random Sequences

Dirk Koopman djk at
Mon Jul 23 10:56:59 BST 2007

Roger Burton West wrote:
> On Mon, Jul 23, 2007 at 09:48:14AM +0100, Mark Blackman wrote:
>> possibly, the obvious thing to do is treat each track like a lottery
>> ball and thus draw it only once until the hopper is exhausted, but would
>> require some way of "refilling" the hopper at some point which is another
>> UI button, so possibly sub-optimal.
> That's the standard approach - starting a random play generates a
> playlist of all tracks, which is then played through.
> The shuffle-playlist generator I wrote tries to avoid having two
> consecutive tracks by the same artist.

Given a limited corpus of songs, the more constraints you place on 
"randomness", the less randomness ensues. The constraint above is, by 
definition, a pattern.

If you want true randomness then you have to accept that you will, from 
time to time, get songs playing next to each other that you didn't want.

This is not a conspiracy. The brain is hardwired to regard this sort of 
thing as suspicious. All our senses are designed to highlight the 
unusual in the here and now. That is our survival mechanism.

Doing the stats on long term trends and proving that, over time, the 
playlists have absolutely no bias of any kind, cuts very little ice in 
the short term. We are not designed, nor are we interested, in the long 
term, other than to extrapolate long term stats into short term paranoia 
because something happens to us, one day, that seems to fit.

This is all about perception of risk. We cope with complete equanimity 
with the fact that 1000's of people die or are severely injured on the 
road every year. Year after year after year. You could easily die 
crossing the road. You are even more likely to die doing something silly 
at home. Yet all we hear/froth about is the possibility of another 
terrorist attack, or some such immediate "different" thing. This is much 
more scary, because it is new, not because large numbers of people 
(compared to everyday risks) die.

We are still hunter gatherers really. We are designed to notice stuff, 
it used to save (some of) our lives.  Get over it, it's the way we work. 
It's just Life.

For the latest PRNG see:, get one online!


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