LINQ in depth

17 steps in 6 sets of C#.

LINQ is the reason C# programmers stop writing loops. It arrived in 2007 as a bet that queries belong in the language, not in strings, and the bet paid off twice: once in method chains that read left to right, and again in a query syntax that reads like the SQL it borrowed from. Both compile to the same calls, and both are lazy — nothing runs until something asks for results.

The basics tour sampled Where and Select. This one covers the rest of the working set: flattening with SelectMany, slicing with TakeWhile and Chunk, the three join shapes, the query keywords let and group into, and the materializers that turn a query into the dictionary you actually wanted. The encore joins, groups and ranks its way through two small reporting programs.

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Shaping

Select with indexThe overload that numbers a list without a counter variable.
SelectManyFlatten a sequence of sequences into one stream.
ZipWalk parallel sequences in step.

Slicing

TakeWhile & SkipWhileCut a sequence at the first element that breaks the rule.
ChunkBatch a sequence into arrays of at most n.
DistinctByDeduplicate by a key while keeping whole elements.

Joins & lookups

JoinThe inner join, matching rows across two sequences on a key.
GroupJoinThe left join's cousin: every left row, with its group of matches.
ToLookupA frozen one-to-many index over a sequence.

Query syntax

Query syntaxThe same LINQ, shaped like the SQL it borrowed from.
let clausesName an intermediate value once, use it three times.
group ... intoGroup inside a query and keep querying over the groups.

Materializing & sets

ToDictionaryMaterialize a query into the collection you will actually use.
Set operationsIntersect, Except and Union treat sequences as sets.
Defaults & generatorsEmpty sequences without the exceptions.

Encore

sales_report.csJoin, group and rank in one query: a sales table from raw orders.
anagram_finder.csGroup words by their sorted letters and the anagrams find themselves.