nule,
или так
<!DOCTYPE HTML>
<html>
<head>
<title></title>
</head>
<body>
<script src="http://code.jquery.com/jquery-latest.js"></script>
<div class=WRP>
<div id=a>id=a</div>
<div id=b>id=b</div>
<div id=b>id=b</div>
<div id=a>id=a</div>
</div>
<script>
var divs_a =$('.WRP div[id="a"]');
var divs_b =$('.WRP div[id="b"]');
divs_a.appendTo('.WRP');
divs_b.appendTo('.WRP')
</script>
</body>
</html>