compare elements of the same List element

Question

I need to compare the same "PhoneNumber" attributes having the same "ID" for each element

 

<List>
      <Connect ID="ID1" PhoneNumber="453585644878">
 
      </Connect>
      <Connect ID="ID1" PhoneNumber="453585644878">
 
      </Connect>
      <Connect ID="ID2" PhoneNumber="45655556658">
       </Connect>
      <Connect ID="ID2" PhoneNumber="96685688787">
      </Connect>
      <Connect ID="ID3" PhoneNumber="5766855577">
      </Connect>
      <Connect ID="ID3" PhoneNumber="8565657787">
      </Connect>
      <Connect ID="ID3" PhoneNumber="4565775235">
      </Connect>
      <Connect ID="ID4" PhoneNumber="44545454545">
      </Connect>
 </List>

 

 

for example in , the first two connect equivalent phone numbers and in the other non-equivalent numbers.