Group by Items in list of objects (Sitecore Item) and bind with Repeater

Question

Sorry for the long description but I want to make it simple for the users to understand my problem. I have a list that contains DepartmentItem and EmployeeItem.

 var empSubRelList = new List<EmpDeptRel>();

internal class EmpDeptRel
{
    public Item DepartmentItem { get; set; }
    public Item EmployeeItem { get; set; }
}

Here is the code that explains how I am adding items to the list:

Item userProfile = Sitecore.Context.Database.GetItem("/sitecore/content/Intranet/User Profiles");

foreach (var subRelItem in userProfile.Axes.GetDescendants().Where(p => p.TemplateID.ToString() == Settings.GetSetting("SubRelTemplateID")
                                                  && p["Subsidiary"] == SubssdiaryItem.ID.ToString()).OrderBy(p => p["Department"]))
{
    empSubRelList.Add(new EmpDeptRel
    {
         DepartmentItem = GetItemById(subRelItem["Department"]),
         EmployeeItem = subRelItem.Parent.Parent
    });       
}

I bind it with a repeater:

repEmployees.DataSource = empSubRelList;
repEmployees.DataBind();

<asp:Repeater runat="server" ID="repEmployees">
   <ItemTemplate>
       <li>
            <%# Name(Eval("DepartmentItem") as Item)%>
            <%# Name(Eval("EmployeeItem") as Item)%>          
       </li>
   </ItemTemplate>

Here is the code for the method "Name()" which is inside the repeater

protected string Name(Item item)
{
    if (item != null)
    {
        return item.Name;
    }
    return string.Empty;
}

the Output is:

IT TestUser1
Administration TestUser2
Administration TestUSer3
Administration TestUser4
Administration TestUser5
Finance TestUSer6

Is it somehow possible to group the list "empSubRelList" With Department So that I can get following output:

IT TestUser1
Administration TestUser2 TestUser3 TestUser4 TestUser5
Finance TestUser6

Answer 1

As Serv wrote, you can do grouping before setting the datasource of your repeater:

IEnumerable<KeyValuePair<string, string>> dataSource = empSubRelList
    .GroupBy(listItem => Name(listItem.DepartmentItem))
    .Select(grouping => new KeyValuePair<string, string>(
        groupping.Key,
        string.Join(", ", grouping.Select(emp => Name(emp.EmployeeItem)))
    ));

repEmployees.DataSource = dataSource;

and then in your html code:

<asp:Repeater runat="server" ID="repEmployees">
   <ItemTemplate>
       <li>
            <%# ((KeyValuePair<string, string>)Container.DataItem).Key %>
            <%# ((KeyValuePair<string, string>)Container.DataItem).Value %>
       </li>
   </ItemTemplate>
</asp:Repeater>