Projection & Grouping

Projection reshapes each element of a sequence into a new shape, and grouping reorganizes a flat sequence into keyed buckets. Together they cover the "what does each row look like in the output?" and "how do I bucket these by category?" questions that show up in almost every LINQ query. This lesson walks through Select, SelectMany, Zip, GroupBy, and ToLookup, with a focus on what each one returns and when to use it.