使用 LINQ 按日期对序列进行无间隙分组

我正在尝试选择列表的一个子组，其中项目具有连续的日期，例如

ID  StaffID  Title              ActivityDate
--  -------  -----------------  ------------
 1       41  Meeting with John    03/06/2010
 2       41  Meeting with John    08/06/2010
 3       41  Meeting Continues    09/06/2010
 4       41  Meeting Continues    10/06/2010
 5       41  Meeting with Kay     14/06/2010
 6       41  Meeting Continues    15/06/2010
  

我每次都使用一个枢轴点，因此将示例枢轴项设为 3，我希望获得以下围绕枢轴产生的连续事件：

ID  StaffID  Title              ActivityDate
--  -------  -----------------  ------------
 2       41  Meeting with John    08/06/2010
 3       41  Meeting Continues    09/06/2010
 4       41  Meeting Continues    10/06/2010
  

我当前的实现是费力地“走进”过去，然后进入未来，以构建列表：

var activity = // item number 3: Meeting Continues (09/06/2010)

var orderedEvents = activities.OrderBy(a => a.ActivityDate).ToArray();

// Walk into the past until a gap is found
var preceedingEvents = orderedEvents.TakeWhile(a => a.ID != activity.ID);
DateTime dayBefore;
var previousEvent = activity;
while (previousEvent != null)
{
    dayBefore = previousEvent.ActivityDate.AddDays(-1).Date;
    previousEvent = preceedingEvents.TakeWhile(a => a.ID != previousEvent.ID).LastOrDefault();
    if (previousEvent != null)
    {
        if (previousEvent.ActivityDate.Date == dayBefore)
            relatedActivities.Insert(0, previousEvent);
        else
            previousEvent = null;
    }
}


// Walk into the future until a gap is found
var followingEvents = orderedEvents.SkipWhile(a => a.ID != activity.ID);
DateTime dayAfter;
var nextEvent = activity;
while (nextEvent != null)
{
    dayAfter = nextEvent.ActivityDate.AddDays(1).Date;
    nextEvent = followingEvents.SkipWhile(a => a.ID != nextEvent.ID).Skip(1).FirstOrDefault();
    if (nextEvent != null)
    {
        if (nextEvent.ActivityDate.Date == dayAfter)
            relatedActivities.Add(nextEvent);
        else
            nextEvent = null;
    }
}

列表relatedActivities然后应该按顺序包含连续的事件。

有没有更好的方法（也许使用 LINQ）？

我有一个想法使用.Aggregate() http://msdn.microsoft.com/en-us/library/system.linq.enumerable.aggregate.aspx但无法想象当它在序列中发现间隙时如何让聚合爆发。

这是一个实现：

public static IEnumerable<IGrouping<int, T>> GroupByContiguous(
  this IEnumerable<T> source,
  Func<T, int> keySelector
)
{
   int keyGroup = Int32.MinValue;
   int currentGroupValue = Int32.MinValue;
   return source
     .Select(t => new {obj = t, key = keySelector(t))
     .OrderBy(x => x.key)
     .GroupBy(x => {
       if (currentGroupValue + 1 < x.key)
       {
         keyGroup = x.key;
       }
       currentGroupValue = x.key;
       return keyGroup;
     }, x => x.obj);
}

您可以通过减法将日期转换为整数，或者想象一个 DateTime 版本（简单）。