Dynamic condition in php

Can someone help me to solved my issue for build dynamic condition in php...

i have an array

$condition = array('FADR1','FADR2','FADR3','SADR1','SADR2','SADR3');

i have tried this code but the result not like i want

for ($i=0; $i < count($condition) ; $i++) {
       if($keydt == $condition[$i]){
              $separator = '';
       }else{
              $separator = '|';
       }
}

i want to make array become like this inside loop

if($keydt == 'FADR1' or $keydt == 'FADR2' or $keydt == 'FADR3' or $keydt == 'SADR1' or $keydt == 'SADR2' or $keydt == 'SADR3'){
     $separator = '';
}else{
     $separator = '|';
}