Linq to Xml: selecting elements if an attribute value equals a node value in an IEnumerable<XElement>

I create an IEnumerable object that just contains the nodes I want from an xml file:

IEnumerable<XElement> rosters = XDocument.Load("roster.xml")
                                         .Elements("rosterlist")
                                         .Elements("roster")
                                         .Where(w => w.Element("division")
                                                      .Value
                                                      .Equals("SUPER AWESOME DIVISION"));

So it's a collection of these:

<rosterlist>
    <roster>
        <userid>1</userid>
        <name></name>
        <etc></etc>
    </roster>
    <roster>
        <userid>2</userid>
        <name></name>
        <etc></etc>
    </roster>
</rosterlist>

I want to grab only the users where the userid attribute is also a userid node within the rosters collection.

IEnumerable<XElement> users = XDocument.Load("user.xml")
                                       .Elements("userlist")
                                       .Elements("user")
                                       .Where(w => rosters.Elements("userid")
                                                          .Contains(w.Attribute("userid").Value));

But it is giving me an error:

The type arguments for method 'System.Linq.Enumerable.Contains(System.Collections.Generic.IEnumerable, TSource)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

What is wrong with my approach?

From stackoverflow

• One issue I see is that in the last code snippet, ...Elements("userid") returns a list of XElement objects which cannot contain a String returned by the Value property. This should work...

  IEnumerable<XElement> rosters = obRoot.Elements("rosterlist").Elements("roster");
  var rosterUserIds = (rosters.Elements("userid").Select(r => r.Value));
  IEnumerable<XElement> users = obRoot.Elements("userlist").Elements("user")
                  .Where(u => rosterUserIds.Contains(u.Attribute("userid").Value));
  

  However I'd do this by using a join query.. Select user join rosters on userid
  It'd go something like this

  string sXml = @"
  <root>
  <rosterlist>
      <roster>
          <userid>1</userid>
          <name>R1</name>
          <etc></etc>
      </roster>
      <roster>
          <userid>2</userid>
          <name>R2</name>
          <etc></etc>
      </roster>
  </rosterlist>
  <userlist>
      <user userid='1'>
          <name>User on roster</name>
      </user>
      <user userid='5'>
          <name>User not on roster</name>
      </user>
  </userlist>
  </root>
  
  ";
  
  XElement obRoot = XElement.Parse( sXml );
  var results = from user in obRoot.Elements("userlist").Elements("user")
     join roster in obRoot.Elements("rosterlist").Elements("roster")
     on user.Attribute("userid").Value equals roster.Element("userid").Value
     select new {Name=user.Element("name").Value, RosterName=roster.Element("name").Value} ;
  
  foreach (var v in results)
  {
     Console.WriteLine("{0, -20} on Roster {1, -20}", v.Name, v.RosterName);
  }
  

  Outputs:

  User on roster       on Roster R1