LINQ GroupBy with Aggregation Returning Unexpected Results When Using Custom Comparer
I'm stuck trying to I'm integrating two systems and I'm testing a new approach and I'm trying to figure out I'm working on a C# project using LINQ to group a list of orders by customer ID and then aggregate the total sales for each customer. However, when using a custom comparer to group by a specific property of the customer objects, the results are not what I expect. I created a custom comparer that compares customer objects based on their `ID` and `Region`, but it seems to be causing unexpected grouping behavior. Here’s the code snippet I’m using: ```csharp public class Customer { public int ID { get; set; } public string Name { get; set; } public string Region { get; set; } } public class CustomerComparer : IEqualityComparer<Customer> { public bool Equals(Customer x, Customer y) { return x.ID == y.ID && x.Region == y.Region; } public int GetHashCode(Customer obj) { return obj.ID.GetHashCode() ^ obj.Region.GetHashCode(); } } var orders = new List<(int OrderID, Customer Customer, decimal Amount)> { (1, new Customer { ID = 1, Name = "Alice", Region = "North" }, 100.00m), (2, new Customer { ID = 1, Name = "Alice", Region = "North" }, 150.00m), (3, new Customer { ID = 2, Name = "Bob", Region = "South" }, 200.00m), }; var result = orders.GroupBy(o => o.Customer, new CustomerComparer()) .Select(g => new { Customer = g.Key, TotalAmount = g.Sum(o => o.Amount) }).ToList(); ``` When I run this code, I expect to see two groups: one for Alice and one for Bob, with their respective total sales. Instead, it seems like Alice’s orders are being aggregated correctly, but I’m not seeing a separate group for Bob. The output is not producing any errors, but the results are not reflecting the expected grouping. I’ve tried checking the implementation of my `GetHashCode` method to ensure it's returning a unique value for different customers, but it doesn’t seem to make a difference. I also verified that the `Region` and `ID` values are correctly assigned. I'm using .NET 6.0, and I'm wondering if there’s something I’m missing regarding how LINQ handles grouping with custom comparers. Any insights or suggestions would be greatly appreciated! Has anyone else encountered this? Hoping someone can shed some light on this. I recently upgraded to C# 3.10. Cheers for any assistance!