Field concatenation based on group in LINQ

Question

I want concate a times field based on grouping of Userid and dates field using LINQ . i am using VS2010 C#(WPF).

i have a collection in below format.

and want result like

Answer 1

You want to GroupBy the UserId, Date and presumably Deptname:

_context.Log.GroupBy(l => new { l.UserId, l.dates.Date, l.Deptname })
            .Select(g => new { g.Key.UserId, g.Key.Date, g.Key.Deptname, Log = string.Join(",", g.Select(i => i.times)) });

Should select the first UserId, Date and Deptname. Then join the log times together. Haven't checked this but seems like it should work.