How do I join 3 enumerable lists that have been grouped?

I have 3 enumerable lists of the same type - they are employee lists. I want to group each of them by month of birth to get something like:
List 1                                      List 2                                  List3
January   |  8.5%                    January  |  5.5%                January   |  9.0%
February |  9.0%                    February |  11.0%              February |  8.0%

Finally I want to unite these lists so that I can bind the results to a combobox which would look something like this:

January   |   8.5%   |   5.5%   |    9.0%
February  |  9.0%   |   11.0%  |   8.0%

var vGroupList1 = (from res in listSource group res by (res.DateOfBirth.Month).ToString());
 double dCount= (from res in listSource 
                                  select res.EmployeeID).Count();
 foreach (var item in vSelection)
                        Employee sd = new Employee ();
                        sd.GroupKey = item.Key;
                        sd.GroupCount = (item.Count() / dCount);
                        foreach (Employee subItem in item)
                            sd.GroupLabel = (String.Format("{0:MMMM}", (subItem.DateOfBirth)));

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Who is Participating?
That was an interesting question indeed, and I am always looking for new challenges using LINQ. I hope this is what you were looking for. You need to concat your collections befor you group them, then group them. I was not able to concat already grouped collections.

I hope this is what you were looking for.
public class EmployeeTest
        public static void Test()
            employee emp1 = new employee("January", 7.5);
            employee emp2 = new employee("January", 5.6);
            employee emp3 = new employee("June", 4.5);
            List<employee> empList1 = new List<employee>();
            employee emp4 = new employee("June", 5.7);
            employee emp5 = new employee("June", 9.5);
            employee emp6 = new employee("January", 6.6);
            List<employee> empList2 = new List<employee>();
            employee emp7 = new employee("June", 6.5);
            employee emp8 = new employee("January", 10.5);
            List<employee> empList3 = new List<employee>();
            var allEmployees = empList1.Concat(empList2).Concat(empList3);
            var grouped = from k in allEmployees group k by k.month into g select g;
            foreach (var group in grouped)
                Console.WriteLine("Scores for " + group.Key);
                foreach (var element in group)
    public class employee
        public string month;
        public double percent;
        public employee(string month, double percent)
            this.month = month;
            this.percent = percent;

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Fernando SotoRetiredCommented:
Can you post the structure of the employee type?
Are the percentages a field in the employee type?
JobbietronicAuthor Commented:
The percentages are calculated at runtime using the count of employees for each month of birth divided by the total number of employees in ech list.
The employee type looks something like this   (the 'Group####' bits are there to allow me to manage the rolled up numbers)          
            public int SchoolID { get; set; }
            public int EmployeeID { get; set; }
            public string DeptName { get; set; }
            public DateTime RegDate { get; set; }
            public string Gender { get; set; }            
            public DateTime DateOfBirth { get; set; }
            public string EntryYear { get; set; }
            public string MotherTongue { get; set; }
            public double SENActive { get; set; }
            public string PrimaryNeed { get; set; }
            public double FSMActive { get; set; }
            public string GroupKey { get; set; }
            public string GroupLabel { get; set; }
            public double GroupCount { get; set; }
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             * Output:
                Scores for January
                Scores for June
JobbietronicAuthor Commented:
Hi Mike, thanks for the reply. The concat and 're-group' is very helpfull. Would you reccomend using a foreach loop to add each of the 12 list items (i.e. months) for each of the three lists into the new employee classes rather than adding them declaratively?
yes you could use a foreach loop or the concat operator, performan-wise I think the concat will be better (I am far from being sure tho).

Btw in the code above I do not "re-group" I just group once after concatenating (spelling?) all the non-grouped lists.
JobbietronicAuthor Commented:
Cheers Mike,
by regroup I meant grouping the concatenated list after I had done the intial grouping to get the percentages.
Thanks again for your help.
JobbietronicAuthor Commented:
Thanks - really helpful and I appreciate the extra information.
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