I am using Laravel 5.2, Is there some best suggestion where to put helper function which is being used just in 1 controller,

I am using Laravel 5.2, I am using a helper function just in 1 controller, where should I put such function

/**
 * trim all elements of array
 * 
 * @param $elements
 * @param string $delimiter
 * @return array
 */
private function trimArrayElements($elements, $delimiter = '|')
{
    return array_map('trim',explode($delimiter, $elements));
}

via Haider Ali