PHP 实现浏览记录并按日期分组

现有测试数据如下，要求实现如下图中的效果：

array(4) {
 [0] => array(6) {
 ["visit_id"] => int(127)
 ["goods_id"] => int(16)
 ["visittime"] => int(1494399935)
 ["goods_name"] => string(53) "OPPO R9s 全网通4G+64G 双卡双待手机 玫瑰金"
 ["shop_price"] => string(6) "500.00"
 }
 [1] => array(6) {
 ["visit_id"] => int(124)
 ["goods_id"] => int(13)
 ["visittime"] => int(1494399921)
 ["goods_name"] => string(76) "SIEMENS/西门子 KA92NV09TI双开门家用对开门电冰箱变频旗舰款"
 ["shop_price"] => string(7) "4000.00"
 }
 [2] => array(6) {
 ["visit_id"] => int(123)
 ["goods_id"] => int(27)
 ["visittime"] => int(1494399903)
 ["goods_name"] => string(85) "爱他美白金版Aptamil 幼儿配方奶粉3段(12-36个月适用)900g(欧洲进口)"
 ["shop_price"] => string(6) "329.00"
 }
 [3] => array(6) {
 ["visit_id"] => int(120)
 ["goods_id"] => int(26)
 ["visittime"] => int(1494224263)
 ["goods_name"] => string(21) "欢乐谷免票一张"
 ["shop_price"] => string(5) "50.00"
 }
}

还没实现之前我想这个代码不知道要O(n)呢还是更高的复杂度才能实现，细想一下，其实php的数组底层就是哈希实现的，如何简单利用这个特性使复杂度降到O(1)呢？

show me the code：

/* 浏览记录按日期分组 */
function groupVisit($visit)
{
 $curyear = date('Y');
 $visit_list = [];
 foreach ($visit as $v) {
  if ($curyear == date('Y', $v['visittime'])) {
   $date = date('m月d日', $v['visittime']);
  } else {
   $date = date('Y年m月d日', $v['visittime']);
  }
  $visit_list[$date][] = $v;
 }
 return $visit_list;
}

说明：入参 $visit 就是上面一开始的测试数据，函数中还对用户体验做了一些优化，比如，你的浏览记录中总是显示出今年的年份，是不是感觉有点冗余，所以如果是本年份的话，年份就要隐藏起来，其他年份还是照样显示出来。不然代码会更加简洁。

好了上面的测试数据经过该函数之后，再把返回值打印出来，有：

array(2) {
 ["05月10日"] => array(3) {
 [0] => array(6) {
  ["visit_id"] => int(127)
  ["goods_id"] => int(16)
  ["visittime"] => int(1494399935)
  ["goods_name"] => string(53) "OPPO R9s 全网通4G+64G 双卡双待手机 玫瑰金"
  ["shop_price"] => string(6) "500.00"
 }
 [1] => array(6) {
  ["visit_id"] => int(124)
  ["goods_id"] => int(13)
  ["visittime"] => int(1494399921)
  ["goods_name"] => string(76) "SIEMENS/西门子 KA92NV09TI双开门家用对开门电冰箱变频旗舰款"
  ["shop_price"] => string(7) "4000.00"
 }
 [2] => array(6) {
  ["visit_id"] => int(123)
  ["goods_id"] => int(27)
  ["visittime"] => int(1494399903)
  ["goods_name"] => string(85) "爱他美白金版Aptamil 幼儿配方奶粉3段(12-36个月适用)900g(欧洲进口)"
  ["shop_price"] => string(6) "329.00"
 }
 }
 ["05月08日"] => array(1) {
 [0] => array(6) {
  ["visit_id"] => int(120)
  ["goods_id"] => int(26)
  ["visittime"] => int(1494224263)
  ["goods_name"] => string(21) "欢乐谷免票一张"
  ["shop_price"] => string(5) "50.00"
 }
 }
}

对的，这正是我想要的效果。