Lambda Queries

Lambda queries are the most flexible and fundamental. In this section, we describe how to chain operators to form more complex queries and introduce several new query operators.

Chaining Query Operators

To build more complex queries, you add additional query operators, creating a chain. For example, the following query extracts all strings containing the letter a, sorts them by length, and then converts the results to uppercase:

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

	IEnumerable<string> query = names
	  .Where   (n => n.Contains ("a"))
	  .OrderBy (n => n.Length)
	  .Select  (n => n.ToUpper( ));

	foreach (string name in query)
	  Console.Write (name + "|");


Where, OrderBy, and Select are all standard query operators that resolve to extension methods in the Enumerable class.

We already introduced the Where operator, which emits a filtered version of the input sequence. The OrderBy operator emits a sorted version of its input sequence; the Select method emits a sequence where each input element is transformed or projected with a given lambda expression (n.ToUpper(), in this case). Data flows from left to right through the chain of operators, so the data is first filtered, then sorted, then projected.


A query operator never alters the input sequence; instead, it returns a new sequence. This is consistent with the functional programming paradigm, from which LINQ was inspired.

Here are the signatures of each of these extension methods (with the ...

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