title: aggregate three same lists based on two columns and sum the third column
body: <p>I have <em>three lists</em> of class type <code>AggClass</code>. I just need to <em>aggregate</em> these <em>three lists</em>.</p>
  <pre><code>public class AggClass
  {
      private string _fan;
      private string _prefix;
      private decimal _amount;
  
      #region Properties
  
      public string Fan
      {
          get { return _fan; }
          set { _fan = value; }
      }
  
      public string Prefix
      {
          get { return _prefix; }
          set { _prefix = value; }
      }
  
      public decimal Amount
      {
          get { return _amount; }
          set { _amount = value; }
      }
      #endregion
  }
  </code></pre>
  <p>If <code>Fan</code> and <code>Prefix</code> columns having same value then I just need make them as one column and <code>Sum</code> the <code>Amount</code>. How to do it?</p>
  <pre><code>LIST 1
  FAN PREFIX   AMOUNT
  F1    P1       10
  F1    P2       20
  F2    P2       50
  
  LIST 2
  FAN PREFIX   AMOUNT
  F1    P1       30
  F1    P3       20
  F2    P2       30
  
  LIST 3
  FAN PREFIX   AMOUNT
  F1    P1       10
  F1    P3       10
  F2    P2       30
  
  OUTPUT
  FAN   PREFIX   AMOUNT
  F1      P1       50
  F1      P2       20
  F1      P3       30
  F2      P2      110
  </code></pre>
  <p>I have to get output like this. How can I concat three lists same time? Is there any best way?</p>