Re: random index in array

You're looking for a shuffle. Once the array is shuffled, you can pull them sequentially. If you don't care if the elements get out of order, use an in-place shuffle. If the order of the elements is important, create a second array of indexes and shuffle that.

my $array = shift;
my $i;
for ($i = @$array; --$i; ) {
    my $j = int rand ($i+1);
    @$array[$i,$j] = @$array[$j,$i];
}
[download]

This is the Fisher-Yates algorithm, shuffles the array in place - very efficient, and lifted straight from perldoc -q shuffle

Comment on Re: random index in array - no duplicates Select or Download Code

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Re: Re: random index in array - no duplicates by samtregar (Abbot) on Jun 07, 2002 at 01:03 UTC
Or simpler still: `use List::Util 'shuffle'; @array = shuffle @array;` [download] -sam	[reply] [d/l]
Re: Re: random index in array - no duplicates by jryan (Vicar) on Jun 08, 2002 at 00:35 UTC
One problem with this, however, is that if the array contains multiple elements with the same value, they will still show up multiple times. Best to filter them out first.	[reply]
Re: Re: Re: random index in array - no duplicates by jsprat (Curate) on Jun 08, 2002 at 06:44 UTC
The OP wrote "but what if I want to be sure that I don't get a duplicate index?" I'm pretty sure he was worrying about pulling the same element twice from the array, not worrying about duplicate elements. If there are duplicate elements, yes he would want to weed them out first.	[reply]