PHP: Delete unique values from an array

Question

I would like to delete all unique values from an array.

So lets say I have $array = (1,2,3,5,4,3,4,5,234)

the function should delete all unique values and output:

$newarray = (3,5,4,3,4,5)

I just thought of a solution with array_count_values but I do not know how I could iterate it. Furthermore I am sure there is a more elegant and efficient way to do this. Thank you for your help in advance.

Answer 1

One of solutions:

$array = [1,2,3,5,4,3,4,5,234];
$freq = array_count_values($array);
print_r(array_filter(
    $array,
    function ($v) use ($freq) { return 1 < $freq[$v]; }
));

Answer 2

$array = (1,2,3,5,4,3,4,5,234);
$freq = array_count_values($array);

$output = array();
foreach($array as $val){
   if($freq[$val] >1){
      $output[] = $val;
   }
}

print_r($output);

May be not the most efficient way.