Joomla : Manage multi selection data

save function
$city = JRequest::getVar( 'cmbcity', '','post', 'int', JREQUEST_ALLOWRAW );
$row->city = implode(",",$city);

insert
$arrloanamt = explode(",",$row->loan_amount);

<? echo in_array($row_amt['loan_amount'], $arrloanamt) ? "selected" : ''; ?>