I had the benefit of a direct discussion with the OP about this, which brought much clarity as to his intentions. He has an array of ~4000 elements and wants to select five non-duplicates out of there. So basically, his code can be reduced to this:

use List::Util 'shuffle';
my %unique = map { $_ => 1 } @weighteddiv;
my @shuffled = shuffle(keys %unique);
@selected = @shuffled[0..4];
[download]

I noticed he was randomizing the array, then selecting random indices from there, which was not only reduntdant but created the issue of potentially selecting the same element.

Update: The big array is *not* already internally unique after all, so I had to add the line to unique it.

Update 2: My solution is no longer relevant, after the OP updated with more information. However, I'm leaving my code as-is because it might help a future monk looking for a similar solution.

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