c# - group list by property and where it appears more than once -

I have a list of type student items.

  Public class student {string FirstName string surname int edge}  

I want that the group students together with the same surname together and Return a list of aliases where an alias appears more than once.

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Here's the code that I am currently using that works but there is a way to return a novel to my Linux statement that is specified to appear more than once?

  var Res = hldList.GroupBy (hld => hld.myid). Ollist (); Foreign currency (var id in reset) {var total = id.Count ();  1) // do something  

SurName and count those that are more than 1:

  var duplicate SurNames = ldList.GroupBy (hld => hld.Surname). Where (g = & gt; g calculation ()> 1). Select (x = & gt; x.Key) .Olist ();