title: Efficient way to remove half of the duplicate items in a list
body: <p>If I have a list say <code>l = [1, 8, 8, 8, 1, 3, 3, 8]</code> and it's guaranteed that every element occurs an even number of times, how do I make a list with all elements of <code>l</code> now occurring <code>n/2</code> times. So since <code>1</code> occurred <code>2</code> times, it should now occur once. Since <code>8</code> occurs <code>4</code> times, it should now occur twice. Since <code>3</code> occurred twice, it should occur once.</p>
  <p>So the new list will be something like <code>k=[1,8,8,3]</code></p>
  <p>What is the fastest way to do this?
  I did <code>list.count()</code> for every element but it was very slow.</p>