Group employees by first letter of name .GroupBy(e => e.Name[0])?

Short answer: var groupedByFirstLetter = employees .Select(g => new { Letter = g.Key, Employees = g.ToList() });

Example code

var groupedByFirstLetter = employees
.Select(g => new { Letter = g.Key, Employees = g.ToList() });

Real-world example (ShopNest)

A sales report joins orders and customers, then GroupBy(c => c.City) to show revenue per city.

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.