I want to hide a field on a node when its value is set to zero using a content type. here is what i had done so far to achieve my goal:
    function pay_nodeapi(&$node, $op, $a3 = NULL, $a4 = NULL)
    {
    	global $user;
    
    if($node->type=='salary_info' && $op=='presave')
    	{
    	 
    	 
    	  $public_holiday = $node->field_sstru_public_holiday[0]['value'];// here i get the value that i set to 0(No) or 1(YES) using a select list. 
    	 
    	  if($public_holiday == 0)
    	  { 
    	    
    		 $nid = node_load(207919); // load node where i want to unset this field
    		
    	unset($nid->field_pd_public_holiday[0]); // here iam wrong and confused 
    		
    	}
    	 else
    	 {
    	  drupal_set_message("HOLIDAY");
    	 }
    	}
what shoul i do to unset my field?