$options = array('code1-AA', 'code1-AB', 'code1-AC', 'code2-AA', 'code2-AD');

foreach ($options as $option) {
    list($optionPart1, $optionPart2) = explode('-', $option);
    $newOptions[$optionPart1][] = $optionPart2;
}

foreach ($newOptions as $code => $codeOptions) {
    $codeLine = $code.' (';
    foreach ($codeOptions as $option) {
        $codeLine .= $option.', ';
    }
    $codeLine = substr($codeLine, 0, -2);
    $codeLine .= ')<br />';
    echo $codeLine;
}

$ancien_code ="";
$nb_options = count($options);
for ($i = 0; $i <$nb_options; $i++)
{
$le_choix = explode("-", $options[$i]);
$code = $le_choix[0];
$valeur = $le_choix[1];
if ()
{
}
}