How to combine many list items into one item?

Question

I have created a class named Impacts:

public class Impacts {
    public Impacts(string _Source, int _Number, string _Target) { 
        this.Source = _Source; 
        this.Number = _Number; 
        this.Target = _Target; 
    }
}

And have created a list of this class:

List<Impacts> ListOfImpacts = new List<Impacts>();

And then, I have added items to the list created:

ListOfImpacts.Add(new Impacts("a" , 1 , "b")); //record 1 
ListOfImpacts.Add(new Impacts("c" , 1 , "d")); //record 2 
ListOfImpacts.Add(new Impacts("d" , 1 , "a")); //record 3 
ListOfImpacts.Add(new Impacts("d" , 1 , "a")); //record 4 
ListOfImpacts.Add(new Impacts("d" , 1 , "a")); //record 5

I want to combine record 3 and record 4 and record 5 since they have the same "Source"="d" and same "Target"="a", so I could have:

new Impacts("d", 3 , "a"); // 3 is the number of iterations of this record 

and delete the three repeated records.

Can someone help me?

Answer 1

var newList = ListOfImpacts.GroupBy(g => new {g.Source, g.Target})
            .Select(g => new Impacts(g.Key.Source, g.Count(), g.Key.Target))
            .ToList();

Live example: http://rextester.com/XOIYM52525

Answer 2

            var newList = ListOfImpacts
            .GroupBy(i => new { i.Source, i.Target })
            .Select(i => new Impacts(i.Key.Source, i.Sum(x => x.Number), i.Key.Target))
            .ToList();