C# 0 The Complete Reference

More Query-Related Extension Methods

In addition to the methods that correspond to the query keywords supported by C#, the 

.NET Framework provides several other query-related extension methods that are often 

helpful in a query. These query-related methods are defined for 

IEnumerable

 by 

Enumerable

. Here is a sampling of several commonly used methods. Because many of the 

methods are overloaded, only their general form is shown.

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Method

Description

All(

condition

)

Returns true if all elements in a sequence satisfy a specified condition.

Any(

condition

)

Returns true if any element in a sequence satisfies a specified condition.

Average( )

Returns the average of the values in a numeric sequence.

Contains(

obj

)

Returns true if the sequence contains the specified object.

Count( )

Returns the length of a sequence. This is the number of elements that it 

contains.

First( )

Returns the first element in a sequence.

Last( )

Returns the last element in a sequence.

Max( )

Returns the maximum value in a sequence.

Min( )

Returns the minimum value in a sequence.

Sum( )

Returns the summation of the values in a numeric sequence.

You have already seen 

Count( )

 in action earlier in this chapter. Here is a program that 

demonstrates the others:

// Use several of the extension methods defined by Enumerable.

using System;

using System.Linq;

class ExtMethods {

  static void Main() {

    int[] nums =  { 3, 1, 2, 5, 4 };

    Console.WriteLine("The minimum value is " + nums.Min());

    Console.WriteLine("The maximum value is " + nums.Max());

    Console.WriteLine("The first value is " + nums.First());

    Console.WriteLine("The last value is " + nums.Last());

    Console.WriteLine("The sum is " + nums.Sum());

    Console.WriteLine("The average is " + nums.Average());

    if(nums.All(n => n > 0))

      Console.WriteLine("All values are greater than zero.");

    if(nums.Any(n => (n % 2) == 0))

      Console.WriteLine("At least one value is even.");

    if(nums.Contains(3))

      Console.WriteLine("The array contains 3.");

  }

}

The output is shown here:

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