c# linq组按日期时间到最近的秒

我想在c#中使用Linq将以下日期时间分组在一起，如下所示:

组1:

2015-03-03 15:18:42.880
2015-03-03 15:18:42.897

组2:

2015-03-19 16:29:59.977
2015-03-19 16:29:59.983
2015-03-19 16:29:59.983

集团3:

2015-03-26 11:27:29.813
2015-03-26 11:27:30.030
2015-03-26 11:27:30.030

第四组:

2015-03-27 15:13:58.483
2015-03-27 15:13:58.483
2015-03-27 15:13:58.500

我对其中一些分组有一个问题。目前，我只是对日期进行分组，忽略毫秒部分。我想要做的是把日期分组，时间间隔在1秒以内，没有毫秒。这是我到目前为止的查询:

var query =
from trans in TransactionTable.AsEnumerable()                                                        
let dateWithoutMilliseconds = trans.Field<DateTime>("TranactionDate").AddMilliseconds(-trans.Field<DateTime>("TranactionDate").Millisecond)
group trans by dateWithoutMilliseconds into g
select new
{                                   
TransDate = g.Key,                                                                
};

DateTime source = ...
...
// Up to nearest second
const int shift = 10000000;
DateTime result = new DateTime(
  (source.Ticks / shift + (source.Ticks % shift >= (shift / 2) ? 1 : 0)) * shift);
// If you want just a key to group by
long key = (source.Ticks / shift + (source.Ticks % shift >= (shift / 2) ? 1 : 0)) * shift;