Your selection_sample routine is not correctly coded. The idea is to randomly select a sample of n elements as you go, there should not be duplicates in the sample. Change your while loop to the following for a more faithful representation of Knuth's algorithm. 
    while ( @results < $num ) {
        if ( (@$array - $pos) * rand() < $num - @results ) {
            push @results, $array->[$pos];
        }
        $pos++;
    }

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In reply to Re: Random Sampling by Anonymous Monk
in thread Random Sampling by demerphq

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