in reply to Shuffle an array

Basically the method works like this.

N is the number of items in the array.

Pick an element from 1 to N at random. Switch that element with the first element.

Now pick an element between 2 and N at random. Switch that element with the second element.

Then pick an element beween 3 and N at random. And switch that element with the third element.

Repeat those two step N-1 times and you have shuffled the array.

If that doesn't explain it for you, try getting a pack of card, put them in order and do the process manually.Even using cards 1 to 6 and a dice, and doing the process a couple of times should clarify things if my words don't help.

In Perl, the counting runs 0 to N-1 each time, but the logic remains the same.

Nah! You're thinking of Simon Templar, originally played (on UKTV) by Roger Moore and later by Ian Ogilvy

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Re: Re: Shuffle an array
by FireBird34 (Pilgrim) on Nov 09, 2002 at 02:06 UTC
    Ah, ok. Make more sense now (yea, I got the N-1 stuff ;)). Didn't exactally know how the whole process worked. Thanks =)
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Re: Re: Shuffle an array
by thinker (Parson) on Nov 09, 2002 at 10:54 UTC
    Hi BrowserUk,

    This doesn't give a fair shuffle. This is well documented, as it is in the FAQ, and is explained well in the Perl Cookbook. A recent node explains it. Check here.

    cheers

    thinker
[reply]

      Are you saying my description is inaccurate? If so, please clarify in what way you think that it is wrong.

      My description is accurate. The link you give chooses a random value from 1 to n each time. My description reduces the range by 1 each time. This is the correct Fisher-Yates technique.

      Nah! You're thinking of Simon Templar, originally played (on UKTV) by Roger Moore and later by Ian Ogilvy
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