$array = [7, 2, 2, 2, 2, 2, 4, 5, 3, 4, 5, 7, 5, 4];
$array_count_values = array_count_values($array);
print_r($array_count_values);
foreach($array_count_values as $key=>$val){
if ($val == 1) {
echo $key;
}
}
/*
run:
Array
(
[7] => 2
[2] => 5
[4] => 3
[5] => 3
[3] => 1
)
3
*/