pluck.php

// $weights = array of weights
// $num = number of result desired.
// returns array of indices chosen from $weights.
function pluck($weights, $num) {
  $chosen = array();
  while (count($chosen) < $num) {
    $sum = array_sum($weights);
    $plucked = rand(1, $sum);
    $count = 0;
    for ($i = 0;
         $i < count($weights) && $count < $plucked;
         $count += $weights[$i++]);
    $chosen[] = --$i;
    $weights[$i] = 0;
  }
  return $chosen;
}

=pluck(array(123, 34, 43, 213, 2, 4, 432), 2);

pluck.rb

class Array
  def sum
    inject {|sum,x| sum+x}
  end

  def pluck(num)
    Array.new(num).fill{pluckElement}
  end

  def pluckElement
    plucked = rand(sum) + 1
    count = 0
    each_with_index{|weight, i|
      if (weight + count >= plucked)
        slice!(i) and return i
      end
      count += weight
    }
  end
end

puts [123, 34, 43, 213, 2, 4, 432].pluck(2)