LINQ Pocket Reference

Quantifiers

Method	Description	SQL equivalents
Contains	Returns true if the input sequence contains the given element	WHERE…IN (…)
Any	Returns true if any elements satisfy the given predicate	WHERE…IN (…)
All	Returns true if all elements satisfy the given predicate	WHERE (…)
SequenceEqual	Returns true if the second sequence has identical elements to the input sequence

Contains and Any

The Contains method accepts an argument of type TSource; Any accepts an optional predicate.

Contains returns true if the given element is present:

	bool isTrue = new int[] { 2, 3, 4}.Contains (3);

Any returns true if the given expression is true for at least one element. We can rewrite the preceding query with Any as follows:

	bool isTrue = new int[] { 2, 3, 4 }.Any (n => n == 3);

Any can do everything that Contains can do, and more:

	bool isFalse = new int[] { 2, 3, 4 }.Any (n => n > 10);

Calling Any without a predicate returns true if the sequence has one or more elements. Here’s another way to write the preceding query:

	bool isFalse = new int[] { 2, 3, 4 }
	               .Where (n => n > 10).Any();

Any is particularly useful in subqueries.

All and SequenceEqual

All returns true if all elements satisfy a predicate. The following returns customers whose purchases are less than $100:

	dataContext.Customers.Where
	  (c => c.Purchases.All (p => p.Price < 100));

SequenceEqual compares two sequences. To return true, each sequence must have identical elements, in the identical order.