LINQ Pocket Reference

Getting Started

The basic units of data in LINQ are sequences and elements. A sequence is any object that implements the generic IEnumerable interface, and an element is each item in the sequence. In the following example, names is a sequence, and Tom, Dick, and Harry are elements:

	string[] names = { "Tom", "Dick", "Harry" };

We call such a sequence a local sequence because it represents a local collection of objects in memory.

A query operator is a method that transforms a sequence. A typical query operator accepts an input sequence and emits a transformed output sequence. In the Enumerable class in System.Linq, there are around 40 query operators, all implemented as static extension methods, called standard query operators.

Note

LINQ also supports sequences that can be dynamically fed from a remote data source such as a SQL Server. These sequences additionally implement the IQueryable<> interface and are supported through a matching set of standard query operators in the Queryable class. For more information, see the upcoming “Interpreted Queries” section.

A query is an expression that transforms sequences with query operators. The simplest query comprises one input sequence and one operator. For instance, we can apply the Where operator on a simple array to extract those whose length is at least four characters as follows:

	string[] names = { "Tom", "Dick", "Harry" };

	IEnumerable<string> filteredNames =
	  System.Linq.Enumerable.Where (
	    names, n => n.Length >= 4); foreach (string n in ...