How to do Count(), Group with QueryExpression/ObservableCollection Result with ASP.NET?

In the original version of this ASP.NET program which is for processing data from Dynamic CRM 365, the QueryExpression Result is transferred to ObservableCollection, then final result in xml format. Now I need to add some count() and group by to the QueryExpression or ObservableCollection. How can I do it? May be with LINQ? Thanks.