PHP Function for array zip merge. Merges two arrays like a zipping. Uneven sized arrays get items appended to the end.

gistfile1.txt

/**
 * Merges two arrays like a zipping. Uneven sized arrays get items 
 * appended to the end. 
 * 
 * @param array $a An array to merge
 * @param array $b Another array to merge
 * @return array An array of merged values
 */
function array_zip_merge(array $a, array $b) {
  $return = array();
  
  $count_a = count($a);
  $count_b = count($b);
  
  if ($count_b < $count_a) {
    // Ensure $b is greater or equal to $a
    $temp = $a;
    $b = $a;
    $a = $temp;
  }
  
  // Zip arrays
  for ($i = 0; $i < $count_a; $i++) {
    $return = array_merge_recursive($return, array_slice($a, $i, 1, true));
    $return = array_merge_recursive($return, array_slice($b, $i, 1, true));
  }
  
  $difference = $count_b - $count_a;
  if ($difference) {
    // There are more items to add on end so pop them at the end
    $return = array_merge_recursive($return, 
      array_slice($b, $count_a, $difference, true));
  }
  
  return $return;
}

The swap function is wrong, it just duplicates the a and doesn't update the counts.

        if ($count_a > $count_b) {
            // Ensure $b is greater or equal to $a
            $temp = $b;
            $b = $a;
            $a = $temp;

            $count_a = count($a);
            $count_b = count($b);
        }

This is a correct implementation