キーと値の関係を維持して、値でソートする。asortは昇順、arsortは降順

$fruits = array("d" => "lemon", "a" => "orange", "b" => "banana", "c" => "apple");
asort($fruits);
foreach ($fruits as $key => $val) {
	echo "$key = $val\n";
}

の結果は

c = apple b = banana d = lemon a = orange