LINQ GroupBy with Substring - Unexpected Grouping Results in C# 10
I'm maintaining legacy code that I'm having a hard time understanding I'm sure I'm missing something obvious here, but I'm encountering an unexpected behavior when using LINQ's `GroupBy` method with a substring on a string property in C#... The goal is to group a list of customer orders by the first three characters of their order IDs, but I'm getting inconsistent grouping results that don't match my expectations. Here's a simplified version of my code: ```csharp public class Order { public string OrderId { get; set; } public decimal Amount { get; set; } } var orders = new List<Order> { new Order { OrderId = "ORD001", Amount = 150 }, new Order { OrderId = "ORD002", Amount = 200 }, new Order { OrderId = "ORD003", Amount = 250 }, new Order { OrderId = "ORD001-01", Amount = 100 } }; var groupedOrders = orders.GroupBy(o => o.OrderId.Substring(0, 3)).ToList(); ``` When I execute this code, I expect to see two groups: one for "ORD" and another for "ORD001-01". Instead, I end up with three groups, with "ORD001-01" being treated as a separate group. This leads to confusion about how `GroupBy` is interpreting the substring. I've tried various approaches, including using `Trim()` and `ToUpper()` to standardize the strings, but the result remains the same. I also verified that the `Substring` method is correctly extracting the first three characters as intended, but the grouping doesn't reflect that. Additionally, when I checked the contents of the groups, the entries seem to be split more than I expected. I'm using .NET 6 and am curious if there's a better way to handle this situation or if there's something I'm overlooking with how `GroupBy` functions with substrings. Any insights or best practices for achieving the desired grouping would be greatly appreciated! I'm working on a CLI tool that needs to handle this. This issue appeared after updating to Csharp LTS.