LINQ：顺序按在册及LT独特的项目数;串＆GT; [英] LINQ: Order By Count of Unique Items in List<string>

问题描述

我有ID列表妥善保存在一个List＆LT;>。我现在需要这个组列表，并获得出现的次数降序排序。

的计数

例如：

 列表＆LT;串GT; aryIDs =新的List＆LT;字符串取代;
aryIDs.Add（1234）;
aryIDs.Add（4321）;
aryIDs.Add（3214）;
aryIDs.Add（1234）;
aryIDs.Add（4321）;
aryIDs.Add（1234）;
 

会产生：

 1234，3
4321，2
3214，1
 

这会很容易在TSQL的，但我想，以避免服务器往返，不必要的表格等如果可能的话。

先谢谢了。

更新：VB.NET转换为以下拉尔夫希林的回答是：

 昏暗的结果=从ID在aryIDs _
                     组ID进行编号入组_
                     顺序按Group.Count（）降序_
                     选择ID，计数= Group.Count（）result.Dump（）
 

解决方案

 列表＆LT;串GT; aryIDs =新的List＆LT;串GT;（）;
aryIDs.Add（1234）;
aryIDs.Add（4321）;
aryIDs.Add（3214）;
aryIDs.Add（1234）;
aryIDs.Add（4321）;
aryIDs.Add（1234）;VAR的结果=从ID在aryIDs
由ID为G组ID
排序依据g.Count（）降
选择新的{ID = g.Key，计数= g.Count（）};result.Dump（）;
 

剪切并粘贴到LinqPad，你应该是好去。

它也可以使用lambda前pressions书面：

  aryIDs.GroupBy（ID =＆GT; ID）.OrderByDescending（ID =＆GT; id.Count（））。选择（G =＆gt;新建{ID = g.Key，计数= g.Count（）}）转储（）;
 

I have a list of ids properly stored in a List<>. I now need to Group this list and get a count of the number of occurrences sorted descending.

Example:

List<string> aryIDs = new List<string>;
aryIDs.Add("1234");
aryIDs.Add("4321");
aryIDs.Add("3214");
aryIDs.Add("1234");
aryIDs.Add("4321");
aryIDs.Add("1234");

Would Produce:

"1234", 3
"4321", 2
"3214", 1

This would be easy in TSQL, but I would like to avoid the server roundtrip, unnecessary tables, etc. if possible.

Thanks in advance.

Update: The VB.NET conversion for Ralph Shillington's answer below:

Dim result = From id In aryIDs _
                     Group id By id Into Group _
                     Order By Group.Count() Descending _
                     Select id, Count = Group.Count()

result.Dump()

解决方案

List<string> aryIDs = new List<string>();
aryIDs.Add("1234");
aryIDs.Add("4321");
aryIDs.Add("3214");
aryIDs.Add("1234");
aryIDs.Add("4321");
aryIDs.Add("1234"); 

var result =     from id in aryIDs
group id by id into g
orderby g.Count() descending
select new { Id=g.Key, Count=g.Count() };

result.Dump();

Cut and paste that into LinqPad and you should be good to go.

It could also be written using Lambda expressions as:

aryIDs.GroupBy (id => id).OrderByDescending (id => id.Count()).Select(g => new { Id=g.Key, Count=g.Count()}).Dump();

这篇关于LINQ：顺序按在册及LT独特的项目数;串＆GT;的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！