How to create a dictionary from a list with duplicate keys?

Short answer: How to create a dictionary from a list with duplicate keys? var dict = employees .GroupBy(e => e.Department) .ToDictionary(g => g.Key, g => g.ToList()); Follow : foreach (var kvp in dict) Console.WriteLine($"{kvp.Key} Department:"); foreach (var emp in kvp.Value) Console.WriteLine($" - {emp.Name}"); Explanation: Group employees by department and convert groups to dictionary entries.

Real-world example (ShopNest)

ShopNest uses LINQ to query orders: filter by date, project to a summary DTO, and order by total—readable C# that becomes SQL under EF Core.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.