组合数组

  /**
     * 组合数组
     * @param  Date  $data 数组
     * @param  Date  $sort_by  排序字段
     * @author liqiuyue
     */
    function composite_array($data,$sort_by){
        $target = array();
        foreach ($data as $val) {
            if (!empty($target)) {  
                if (in_array($val[$sort_by], array_keys($target))) {  
                    $target[$val[$sort_by]][] = $val;  
                } else {  
                    $target[$val[$sort_by]][] = $val;  
                }  
            } else {  
                $target[$val[$sort_by]][] = $val;  
            } 
        }
        return $target;
    }