LINQ Pocket Reference

Element Operators

Method	Description	SQL equivalents
First, FirstOrDefault	Returns the first element in the sequence, optionally satisfying a predicate	SELECT TOP 1…ORDER BY…
Last, LastOrDefault	Returns the last element in the sequence, optionally satisfying a predicate	SELECT TOP 1…ORDER BY…DESC
Single, SingleOrDefault	Equivalent to First/ FirstOrDefault, but throws an exception if there is more than one match
ElementAt, ElementAtOrDefault	Returns the element at the specified position	Exception thrown
DefaultIfEmpty	Returns null or default(TSource) if the sequence has no elements	OUTER JOIN

Methods ending in “OrDefault” return default(TSource) rather than throw an exception if the input sequence is empty, or if no elements match the supplied predicate.

default(TSource) = null for reference type elements, or “blank” (usually zero) for value type elements.

First, Last, Single

Argument	Type
Source sequence	IEnumerable<TSource>
Predicate (optional)	TSource => bool

The following example demonstrates First and Last:

	int[] numbers  = { 1, 2, 3, 4, 5 };
	int first      = numbers.First();                  // 1
	int last       = numbers.Last();                   // 5
	int firstEven  = numbers.First (n => n % 2 == 0);  // 2
	int lastEven   = numbers.Last  (n => n % 2 == 0);  // 4

The following demonstrates First versus FirstOrDefault:

	// Throws an exception:
	int firstBigError = numbers.First (n => n> 10);

	// Evaluates to 0:
	int firstBigNumber =numbers.FirstOrDefault(n => n > 10);

To avoid an exception, Single requires exactly one matching element;