Lambda Expressions

The standard query operators are implemented as extension methods we can call them directly, as though they were instance methods.

string[] words = { "one", "four",  "seven" }; 
IEnumerable<string> filteredWords = words.Where (n => n.Length >= 4); 

Most query operators accept a lambda expression as an argument

The following query extracts all words that contain the letter "o".

IEnumerable<string> filteredWords = words.Where (n => n.Contains("o") ); 

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

Extension Methods with Chaining

string[] words = { "one", "two", "three", "four", "six", "seven" }; 

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

Extension Methods without Chaining

IEnumerable<string> filter = words   .Where    (n => n.Contains("o")) 
IEnumerable<string> sorted = filter  .OrderBy  (n => n.Length); 
IEnumerable<string> result = sorted  .Select   (n => n.ToUpper()); 

No Extension Methods with Chaining

IEnumerable<string> filter = 
  Enumerable.Select ( 
    Enumerable.OrderBy ( 
      Enumerable.Where ( 
        words, n => n.Contains("o") 
      ), n => n.Length 
    ), n => n.ToUpper() 
  ); 

No Extension Methods without Chaining

IEnumerable<string> filter = Enumerable.Where    (words, n => n.Contains("o")); 
IEnumerable<string> sorted = Enumerable.OrderBy  (filter, n => n.Length) 
IEnumerable<string> result = Enumerable.Select   (sorted, n => n.ToUpper());