PHP how to remove all other operators except -
===

i want to remove all other operators except -. i worked on the following but stuck here. 

    $s1 = "Hello@*&^%$#@!)({}[]?.,<> dis$ is. testing -";
    $s2 = "- i love% the way. it, works";

    for($ii=0;$ii<3;$ii++){

    $from = array('/\(|\)/','/\d+ml|\d+g/','/\s+/'); 
    $to = array('','','-'); 

    $sample=${'s' . $ii}; 

    $sample = strtolower(trim(preg_replace($from,$to,$sample),'-')); 
    echo $sample."<br>";

    }

please help me in this regards.


**Output required**

    hello-dis-is-testing
    i-love-the-way-it-works

