如何在Java中执行（sql）组(How to perform a group by (sql) in Java)

如何在Java中执行（sql）组(How to perform a group by (sql) in Java)

我有一个文本文件，如下所示：

code appearance ---------------- j4t8 1 fj89 3 pf6n 1 j4t8 5

我想按照看起来最多的代码进行排序。 正如您所看到的（并且由于我想执行分组），存在重复的代码，因此使用HashMap会出现问题（重复键）。 有任何想法吗？

I have a text file which looks like this:

code appearance ---------------- j4t8 1 fj89 3 pf6n 1 j4t8 5

And I want to sort by the codes which appear the most. As you can see (and since I want to perform a group by) there are duplicate codes, so using HashMap would be a problem (duplicate keys). Any ideas?

最满意答案

不知道这是否是最好的解决方案，但你可以创建一个列表的地图，如下所示：

Map<String, List<Integer>> map = new HahsMap<String, List<Integer>>(); if(map.contains.(key)) { map.get(key).add(new_appearance_value); } else { List<Integer> app = new ArrayList<Integer>(); app.add(new_appearance_value); map.put(key, app); }

地图键将是代码，外观的值将进入列表。

注意：要确定哪些代码具有更多外观，只需检查每个代码列表的大小。

don't know if this is the best solution but you could create a map of a list like this:

Map<String, List<Integer>> map = new HahsMap<String, List<Integer>>(); if(map.contains.(key)) { map.get(key).add(new_appearance_value); } else { List<Integer> app = new ArrayList<Integer>(); app.add(new_appearance_value); map.put(key, app); }

Where the map key would be the code and the values of appearance would go into the list.

Note: to determine which code has more appearances just check for the size of the list of each code.