All 18 LINQ questions
More in LINQ
What is LINQ, and what are the two main syntax styles you can use to write a LINQ query? What is the difference between Where() and Select() in a LINQ query? What is the difference between IEnumerable and IQueryable in LINQ? What is the difference between First, FirstOrDefault and Single? What is 'deferred execution' in LINQ, and how does it differ from calling .ToList() or .ToArray() immediately? How do GroupBy() and its resulting IGrouping<TKey, TElement> work? What is the difference between First(), FirstOrDefault(), Single(), and SingleOrDefault()? What is LINQ, and how does it simplify querying collections compared to writing manual loops? What is the difference between IEnumerable<T>, IQueryable<T>, and List<T>, and how does choosing the wrong one hurt performance against a database? How does GroupBy translate and what performance pitfalls exist?
Advertisement
C# › LINQ

What is the difference between Select and SelectMany?

Intermediate

Answer

Select projects one-to-one (giving a sequence of sequences if the selector returns a collection); SelectMany flattens those into one sequence.
var tags = posts.Select(p => p.Tags);     // IEnumerable<List<string>>
var flat = posts.SelectMany(p => p.Tags); // IEnumerable<string>
Real-world example Getting one flat list of all line items across all orders.
All 18 LINQ questions