Как убрать из слова нижнее подчеркивание?

$str = 'connected_categories';

$result = explode("_",  $str);
$word_one = $result[0];
$word_two = ucfirst($result[1]);

$final = $word_one . $word_two;

function changeToCamelCase(string $str)
{
    $explodeString = explode('_', $str);
    $maxCount      = count($explodeString);

    for ($i = 1; $i < $maxCount; $i++) {
        $explodeString[$i] = ucfirst($explodeString[$i]);
    }

    return implode($explodeString);
}

$string    = 'connected_categories';
$newString = changeToCamelCase($string);

echo $newString;