Writing a New Query Operator

Although the standard query operators supplied are comprehensive, there is often the need to build more operators to satisfy a programming problem at hand. LINQ to Object operators are in their purest form, extension methods that add functionality to any IEnumerable<T> collection type. Although writing new operators might seem ambitious at first, the implementation code for the standard query operators supplied by Microsoft rarely span more than a few lines, and it is unlikely your custom operators will be any more complex.

Query operators for LINQ to Objects fall into four categories based on their return type and action. The basic operator categories are