这种判断必须得保证后台数据的键值为数字 ，反正要能跟数字计算的数据才行
ts2.php
<?php
$array = array('0'=>'a1','1'=>'b1','2'=>'c1','3'=>'d1','4'=>'e1','5'=>'f1');//print_r($array)
?>
ts3.php
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<script src="js/jquery-2.1.1.min.js"></script>
<style type="text/css">
.q{color: red}
.w{color: blue}
.e{color: black}
</style>
<body>
<?php include 'ts2.php'; ?>
<ul>
<?php foreach ($array as $k => $v) { ?>
<?php if(($k+1)%3==1){ ?>
<li class="q"><?php echo $k;?></li>
<?php } ?>
<?php if(($k+1)%3==2){?>
<li class="w"><?php echo $k;?></li>
<?php } ?>
<?php if(($k+1)%3==0){?>
<li class="e"><?php echo $k;?></li>
<?php } ?>
<?php } ?>
</ul>
<!-- <ul>
<li class="q"></li>
<li class="w"></li>
<li class="e"></li>
<li class="q"></li>
<li class="w"></li>
<li class="e"></li>
</ul> -->
</body>
</html>