Trying GroupBy within List in c#

Question

In the below case, I want to get a count of how many times the employee is repeating. For example, if the list has EmpA 25 times, I would like to get it. I am trying with GroupBy but not getting results. I can do record skip and find the count but there are lot of records.

So in below example, lineEmpNrs is the list and I want to have grouping results by employee ID.

Please suggest.

public static string ReadLines(StreamReader input)
{
string line;
while ( (line = input.ReadLine()) != null)
   yield return line;

}

private taMibMsftEmpDetails BuildLine(string EmpId, string EmpName, String ExpnsDate)
{
taMibMsftEmpDetails empSlNr = new taMibMsftEmpDetails();
empSlNr.EmployeeId  = EmpId;
empSlNr.EmployeeName   = EmpName;
empSlNr.ExpenseDate = ExpnsDate;
return empSlNr;

}

List<taMibMsftEmpDetails> lineEmpNrs = new List<taMibMsftEmpDetails>();
foreach (string line in ReadLines(HeaderFile))
{ 
headerFields = line.Split(',');
lineEmpNrs.Add(BuildLine(headerFields[1],headerFields[2],headerFields[3]));
}

Answer 1

You can define following delegate, which you will use to select grouping key from list elements. It matches any method which accepts one argument and returns some value (key value):

public delegate TResult Func<T, TResult>(T arg);

And following generic method, which will convert any list to dictionary of grouped items

public static Dictionary<TKey, List<T>> ToDictionary<T, TKey>(
    List<T> source, Func<T, TKey> keySelector)
{
    Dictionary<TKey, List<T>> result = new Dictionary<TKey, List<T>>();

    foreach (T item in source)
    {
        TKey key = keySelector(item);
        if (!result.ContainsKey(key))
            result[key] = new List<T>();
        result[key].Add(item);
    }

    return result;
}

Now you will be able to group any list into dictionary by any property of list items:

List<taMibMsftEmpDetails> lineEmpNrs = new List<taMibMsftEmpDetails>();
// we are grouping by EmployeeId here
Func<taMibMsftEmpDetails, int> keySelector = 
    delegate(taMibMsftEmpDetails emp) { return emp.EmployeeId; };

Dictionary<int, List<taMibMsftEmpDetails>> groupedEmployees = 
    ToDictionary(lineEmpNrs, keySelector);

Answer 2

GroupBy should work if you use it like this:

var foo = lineEmpNrs.GroupBy(e => e.Id);

And if you'd want to get an enumerable with all the employees of the specified ID:

var list = lineEmpNrs.Where(e => e.Id == 1); // Or whatever employee ID you want to match

Combining the two should get you the results you're after.

Answer 3

If you wanted to see how many records there were with each employee, you can use GroupBy as:

foreach (var g in lineEmpNrs.GroupBy(e => e.Id))
{
  Console.WriteLine("{0} records with Id '{1}'", g.Count(), g.Key);
}

To simply find out how many records there are for a specified Id, however, it may be simpler to use Where instead:

Console.WriteLine("{0} records with Id '{1}'", lineEmpNrs.Where(e => e.Id == id).Count(), id);