Re: How do I shuffle an array?


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Re: How do I shuffle an array?

by rajib (Novice)

on Aug 20, 2002 at 18:13 UTC ( [id://191540]=note: print w/replies, xml )

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in reply to How do I shuffle an array?


shuffle( \@array );

sub shuffle
{
  my $array = shift;

  for ( my $i = 0; $i <= $#array; ++$i )
  {
    my $rand = rand($#array);
    @$array[$i,$rand] = @$array[$rand,$i];
  }
}
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{Editor's note: This solution is flawed. Read Abigail-II's reply, Re: Answer: How do I shuffle an array?, for an explanation.}

Comment on Re: How do I shuffle an array? Download Code

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Re: Answer: How do I shuffle an array?
by Abigail-II (Bishop) on Aug 21, 2002 at 09:53 UTC

$rand

rand $#array

$rand

rand @array

Let the size of the array be N. Then at each iteration, you select from N elements (after the fix given above), and change it with the one on position $i. You do this N times. Hence, you will get N^N different outcomes. There are however, only N! different permutations of the array. And since N! isn't a divisor of N^N for N > 2, some outcomes will be favoured over others by your algorithm.

Please use the Fisher-Yates shuffle as described in the FAQ. That one is fair.

Abigail

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