public int CId { get; set; }
public int PId { get; set; }
public int Cnt { get; set; }
public static void Main()
Item[] array = new Item[3] {
new Item { CId = 1, PId = 100, Cnt = 5 },
new Item { CId = 1, PId = 100, Cnt = 1 },
new Item { CId = 2, PId = 100, Cnt = 7 }
var result = array.GroupBy(x => new { x.CId, x.PId })
.Select(g => new Item { CId = g.Key.CId, PId = g.Key.PId, Cnt = g.Sum(x => x.Cnt) });
foreach(var item in result)
Console.WriteLine($"CId: {item.CId}, PId: {item.PId}, Cnt: {item.Cnt}");