c# - How to GroupBy/GroupJoin XElements using LINQ -

I have been killed with the query Please help me.

I have an XML

  & lt; Set type = "main" & gt; & Lt; FirstUnit xmlns: i = "http://www.w3.org/2001/XMLSchema-instance" z: id = "i1" xmlns: z = "http://schemas.microsoft.com/2003/10/ ordering / "& Gt; & Lt; CreateDate & gt; 2013-06-06T13: 19: 17.457 & lt; / CreateDate & gt; & Lt; PrimaryKey & gt; 1 & lt; / PrimaryKey & gt; & Lt; / FirstUnit & gt; & Lt; Secondinit xmlns: i = "http://www.w3.org/2001/XMLSchema-instance" z: id = "i1" xmlns: z = "http://schemas.microsoft.com/2003/10/ ordering / "& Gt; & Lt; CreateDate & gt; 2013-06-06T13: 19: 17.457 & lt; / CreateDate & gt; & Lt; PrimaryKey & gt; 1 & lt; / PrimaryKey & gt; & Lt; Exercise & gt; Test & lt; / Exercise & gt; & Lt; / SecondUnit & gt; & Lt; FirstUnit xmlns: i = "http://www.w3.org/2001/XMLSchema-instance" z: id = "i1" xmlns: z = "http://schemas.microsoft.com/2003/10/ ordering / "& Gt; & Lt; CreateDate & gt; 2013-06-06T13: 19: 17.457 & lt; / CreateDate & gt; & Lt; PrimaryKey & gt; 2 & lt; / PrimaryKey & gt; & Lt; / FirstUnit & gt; & Lt; Secondinit xmlns: i = "http://www.w3.org/2001/XMLSchema-instance" z: id = "i1" xmlns: z = "http://schemas.microsoft.com/2003/10/ ordering / "& Gt; & Lt; CreateDate & gt; 2013-06-06T13: 19: 17.457 & lt; / CreateDate & gt; & Lt; PrimaryKey & gt; 2 & lt; / PrimaryKey & gt; & Lt; Exercise & gt; Test & lt; / Exercise & gt; & Lt; / SecondUnit & gt; & Lt; / Set & gt;   
 Now I want to group the unit based on the primary key which I want. I.e FirstUnit and SecondUnit in a group the  primary key & gt; The node value should be "1" and the second group with the  PrimaryKey  node value "2".  
 I have tried to do it with the following question, yet it needs to be more refined,  
  var element = xDocument.GroupBy (a => A.Elements () .Decundents (). Where (x => x.Name.LocalName == "Primary") .Oolist ());   
 Thanks in advance.   
 
 
 It seems that you just need group by  value  Is:  
  // If & lt; Set & gt; Document element, change the descendant ("Set") to the root level elements = xDocument.Descendants ("Set"). Elements () .GroupBy (x => x.Element ("PrimaryKey"));   
 (If necessary, provide a namespace for the element - use a  where  the rule to check the local name is slightly ugly.) < / P> 
 If this does not work for you, please provide more information about what you are trying to do.