C# 5.0 Programmer's Reference

182 ❘ CHAPTER 8 LINQ
The following list summarizes LINQ’s aggregate methods.
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Aggregate—Uses a method that you specify to perform some calculation on the values
Average—Returns the average of the values
Count—Returns the number of items that satisfy a condition
Sum—Returns the sum of the values
LongCount—Returns the number of items that satisfy a condition as a long
Max—Returns the maximum value
Min—Returns the minimum value
Set Methods
Set methods modify a set of items. For example, the Union method creates the union of two sets.
C# does not provide a special syntax for including these methods in a LINQ query, so you must
invoke the methods directly. Fortunately these methods are easy to use.
For example, suppose the ordersPaid and ordersDue arrays contain Order objects representing
customer orders that have been paid and that are due, respectively. The following statement uses
the Union method to create a new array containing all the orders in both arrays.
Order[] allOrders = ordersPaid.Union(ordersDue).ToArray();
The result of the Union method is an iterator that you could loop over with a foreach statement.
This example calls the result’s ToArray method to convert it into an array.
You can apply these methods to the results of a query. For example, the following query examines
the orders array and selects the Order objects’ CustomerId values. The code then uses the Distinct
method to restrict the result to only distinct values. The following foreach statement displays the
distinct values.
var query =
(from order in orders select order.CustomerId).Distinct();
foreach (int id in query)
Console.WriteLine(id);
The following list summarizes LINQ’s set methods.
Concat—Returns two result sets concatenated
Distinct—Returns a set without duplicates
Except—Returns the items in one set except those that are also in a second set
Intersect—Returns the items that are in both of two set
Union—Returns the items that are in either of two set
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