1、使用Linq的OrderBy进行排序

List<string> a = new List<string> { "b", "c", "a", "aa" };
var b = a.OrderBy(o => o).ToList();
//使用区域敏感排序规则和固定区域比较字符串。
var b = a.OrderBy(o => o, StringComparer.InvariantCulture).ToList();
//使用区域敏感排序规则、固定区域来比较字符串，同时忽略被比较字符串的大小写。
var b = a.OrderBy(o => o, StringComparer.InvariantCultureIgnoreCase).ToList();

2、使用Linq的group by进行分组

示例数据：

ID  Counter  SrvID FirstName
--  ------   ----- ---------  
1   34       66M   James
5   34       66M   Keith
3   55       45Q   Jason
2   45       75W   Mike
4   33       77U   Will

list1.GroupBy(item => new { Counter = item.Counter, SrvID = item.SrvID })
     .Select(group => new { 
        ID = group.First().ID, 
        Counter = group.Key.Counter,
        SrvID = group.Key.SrvID,
        FirstName = group.First().FirstName})
     .OrderBy(item => item.ID);

或者

var query =
  from record in list1
  group record by new {record.Counter, record.SrvID } into g
  let winner =
  (
    from groupedItem in g
    order by groupedItem.ID
    select groupedItem
  ).First()
  select winner;

或者

var otherQuery = list1
  .GroupBy(record => new {record.Counter, record.SrvID })
  .Select(g => g.OrderBy(record => record.ID).First());

分组后数据：

ID  Counter  SrvID FirstName
--  ------   ----- ---------  
1   34       66M   James
2   45       75W   Mike
3   55       45Q   Jason
4   33       77U   Will

相关文档：.NET(C#) System.Linq中实现多列group by(分组)的示例代码