This function should REALLY come in handy for a lot of folks (heavy sarcasm). It calculates all size 2 subsets of an array whose values are unique, and in no particular order. So, passing it an array of [1,2,3] will return [[1,2],[1,3],[2,3]]. Passing it an array of [1,2,3,2,1,2,3] will return exactly the same thing. Go wild!

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function get_distinct_size_2_subsets($array)
{
  $subsets = array();

  // if the array only contains two or less element, just return it
  if (count($array) <= 2)
    return $array;

  for ($i=0; $i<count($array); $i++)
  {
    $curr_el1 = $array[$i];

    for ($j=0; $j<count($array); $j++)
    {
      $curr_el2 = $array[$j];

      if ($curr_el1 == $curr_el2)
        continue;

      // if an element of [$curr_el1, $curr_el2] and [$curr_el2, $curr_el1] doesn't exist,
      // add if to $subsets
      if (!in_array(array($curr_el1, $curr_el2), $subsets) && !in_array(array($curr_el2, $curr_el1), $subsets))
        $subsets[] = array($curr_el1, $curr_el2);
    }
  }

  return $subsets;
}