Get non-repeated characters in string and count them

I need to process a string like abclkjabc and return only 3 which counts characters l, k, and j.

I've tried this.

$stringArr = [];
foreach(str_split($string) as $pwd) {
   if(!in_array($pwd, $stringArr)) {
      $stringArr[] = $pwd;
   }
}
$uniqChar = count($stringArr);

Try the following instead:

function getNonRepeatingCharacters($str) {
    $counter = [];
    $spllitted = str_split($str);
    foreach($spllitted as $s) {
        if(!isset($counter[$s])) $counter[$s] = 0;
        $counter[$s]++;
    }
    $non_repeating = array_keys(array_filter($counter, function($c) {
        return $c == 1;
    }));

    return $non_repeating;
}

$string = "abclkjabc";
$handle = getNonRepeatingCharacters($string);