Use SelectMany to flatten nested collections?

Short answer: Use SelectMany to flatten nested collections var nested = new List<List<string>> { new() { "A", "B" }, new() { "C", "D" } var flat = nested.SelectMany(x => x); Use SelectMany to flatten nested collections var nested = new List<List<string>> { new() { "A", "B" }, new() { "C", "D" } var flat = nested.SelectMany(x => x); Real-world… example (ShopNest)… ShopNest… maps entities to DTOs with .Select(o => new…

Explain a bit more

OrderSummaryDto { Id = o.Id, Total = o.Total }) so the API does not leak internal fields. Use SelectMany to flatten nested collections var nested = new List<List<string>> { new() { "A", "B" }, new() { "C", "D" } var flat = nested.SelectMany(x => x); Use SelectMany to flatten nested collections var nested = new List<List<string>> { new() { "A", "B" }, new() { "C", "D" } var flat = nested.SelectMany(x => x); Real-world… example (ShopNest) ShopNest maps entities to DTOs with .Select(o => new OrderSummaryDto { Id = o.Id, Total = o.Total }) so the API does not leak internal fields.

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.