aggregate two same lists based on two columns and sum the third column

Question

i have two lists of class type TestClass. I just need to aggregate two lists.

 public class TestClass
{
    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
}

If Fan and Prefix columns have same value then i just need make them as one column and sum the amount. How to do it?

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

OUTPUT
FAN   PREFIX   AMOUNT
F1    P1       40
F1    P2       20
F1    P3       20
F2    P2       80

I need output like this. What is the best way to achieve this?

Answer 1

var l1 = new List<TestClass>
{
    new TestClass{Fan = "F1", Prefix = "P1", Amount = 10},
    new TestClass{Fan = "F1", Prefix = "P2", Amount = 20},
    new TestClass{Fan = "F2", Prefix = "P2", Amount = 50},
};

var l2 = new List<TestClass>
{
    new TestClass{Fan = "F1", Prefix = "P1", Amount = 30},
    new TestClass{Fan = "F1", Prefix = "P3", Amount = 20},
    new TestClass{Fan = "F2", Prefix = "P2", Amount = 30},
};

var result = l1.Concat(l2).GroupBy(f => new { f.Fan, f.Prefix })
               .Select(g => new TestClass 
                            {
                                Fan = g.Key.Fan, 
                                Prefix = g.Key.Prefix, 
                                Amount = g.Sum(_ => _.Amount) 
                            })
               .ToList();
//Fan  Prefix  Amount
//F1   P1      40 
//F1   P2      20 
//F2   P2      80 
//F1   P3      20 

First we put the two lists together (List.Concat), then group elements that have the same Fan and Prefix together (GroupBy) and finally we sum up the amounts per group.