Group list entries with LINQ

Question

I have the following model:

public class Entry
{
    public int UseraccountId { get; set; }
    public int CompanyId { get; set; }
    public DateTime CreationDate { get; set; }
    public string Target { get; set; }
    public string Message { get; set; }
}

And a list with a lot of entries:

List<Entry> entries = ... //get all entries.

Example:

I'd now like row 2 and 3 to be grouped because they have the same UserId, same CompanyId, same target and almost (and this is the difficult part), let's say in a range of 5 seconds, the same date time.

After grouping my list should look like this:

Is there any easy approach for this problem? Any advices? I bet Linq will help me around but I'm not sure how.

Edit: Thank you all for your feedback. I decided to change the design and to ensure that the datetime is now really the same. So grouping with linq is now very easy.

Answer 1

As @dtb menitons, grouping by "close" is difficult because you can end up with a bigger "bucket" than you intended. For example, If you have 100 entries that are created 4 seconds apart from each other, grouping items that are within 5 seconds of the "next" item would put all of them in one bucket!

If, however, you want to round the creating date to the nearest, say, 5 seconds and then group, you could use:

TimeSpan ts = new TimeSpan(0, 0, 5);  // 5 seconds
entries.GroupBy(i => new {
                          UserId = i.UserId, 
                          CompanyId = i.CompanyId, 
                          Target = i.Target, 
                          RoundedTime = DateTime.MinValue.AddTicks(
                                            (long)(Math.Round((decimal)i.CreationDate.Ticks / ts.Ticks) * ts.Ticks)
                                        ) ;
                          ))
       .Select(g => new {
                         UserId = g.Key.UserId, 
                         CompanyId = g.Key.CompanyId, 
                         Target = g.Key.Target, 
                         RoundedTime = g.Key.RoundedTime,
                         Message = string.Join(", ",g.Select(i=> i.Message).ToArray())
                        } );

That will group by items that are rounded to the nearest 5 seconds - it's possible that two items one second apart will be in different buckets, but you don't have the problem with cummutativity that your stated requirement has.