LINQ之Max

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Max()

使用Max()以获得序列中最大的元素。 MSDN

诸如int类型或float类型等使用Max()求最大值非常简单。

public static decimal Max( this IEnumerable source ); public static double Max( this IEnumerable source ); public static float Max( this IEnumerable source ); public static int Max( this IEnumerable source ); public static long Max( this IEnumerable source );

代码示例：

public static class Program
{
    static void Main( string[] args )
    {
        int[]       intNumbers      = new int[]     { 1, 4, 3, 4 };
        float[]     floatNumbers    = new float[]   { 1.0f, 3.0f, 6.0f };

        int     intMax      = intNumbers.Max();
        float   floatMax    = floatNumbers.Max();

        System.Console.WriteLine( "intNumbers:{0}",   intNumbers.Text() );
        System.Console.WriteLine( "最大:{0}",         intMax );

        System.Console.WriteLine( "floatNumbers:{0}",   floatNumbers.Text() );
        System.Console.WriteLine( "最大:{0}",           floatMax );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
}

intNumbers:[1], [4], [3], [4],
最大:4
floatNumbers:[1], [3], [6],
最大:6

Max()支持数字类型为null。

代码示例：

public static class Program
{
    static void Main( string[] args )
    {
        int?[]      intNumbers      = new int?[]    { 1, null, 3, null };
        float?[]    floatNumbers    = new float?[]  { null, null, null };

        int?    intMax      = intNumbers.Max();
        float?  floatMax    = floatNumbers.Max();

        System.Console.WriteLine( "intNumbers:{0}",   intNumbers.Text() );
        System.Console.WriteLine( "最大:{0}",         intMax );

        System.Console.WriteLine( "floatNumbers:{0}",   floatNumbers.Text() );
        System.Console.WriteLine( "最大:{0}",           floatMax );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
}

intNumbers:[1], , [3], ,
最大:3
floatNumbers:, , [],
最大:

对于非数字类型的自定义类型，我们可以通过设定条件进行对比。

public static decimal Max( this IEnumerable source, Func selector ); public static double Max( this IEnumerable source, Func selector ); public static float Max( this IEnumerable source, Func selector ); public static int Max( this IEnumerable source, Func selector ); public static long Max( this IEnumerable source, Func selector );

代码示例：

public static class Program
{
    private class Parameter
    {
        public string   Name    { get; set; }
        public int      Age     { get; set; }
        
        public override string
        {
            return string.Format( "Name:{0}, Age:{1}"
        }
    }

    static void Main( string
    {
        Parameter[] parameters = new
        {
            new Parameter() { Age = 52, Name = "正一郎" },
            new Parameter() { Age = 28, Name = "清次郎" },
            new Parameter() { Age = 20, Name = "誠三郎" },
            new Parameter() { Age = 18, Name = "征史郎" },
        };

        int maxAge = parameters.Max( value => value.Age );

        System.Console.WriteLine( "parameters:{0}", parameters.Text() );
        System.Console.WriteLine( "最大年龄:{0}", maxAge );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
}

parameters:[Name:正一郎, Age:52], [Name:清次郎, Age:28], [Name:誠三郎, Age:20],
[Name:征史郎, Age:18],
最大年龄:52

如果想要自定义类直接使用Max()，可以通过继承IComparable实现其中的CompareTo自定义比较方法。 IComparable

代码示例：

public static class Program
{
    private class Parameter : System.IComparable
    {
        public string   Name    { get; set; }
        public int      Age     { get; set; }
        
        public override string ToString()
        {
            return string.Format( "Name:{0}, Age:{1}", Name, Age );
        }

        // 实现接口中的比较方法
        //  0 相等
        // -1 小于目标
        //  1 大于目标
        public int CompareTo( Parameter i_other )
        {
            int thisNum     = this.Age + this.Name.Length;
            int otherNum    = i_other.Age + i_other.Name.Length;
            
            if( thisNum == otherNum )
            {
                return 0;
            }

            if( thisNum > otherNum )
            {
                return 1;
            }
            return -1;
        }
    }

    static void Main( string[] args )
    {
        Parameter[] parameters = new Parameter[]
        {
            new Parameter() { Age = 52, Name = "正一郎" },
            new Parameter() { Age = 28, Name = "清次郎" },
            new Parameter() { Age = 20, Name = "誠三郎" },
            new Parameter() { Age = 18, Name = "征史郎" },
        };

        Parameter max   = parameters.Max();

        System.Console.WriteLine( "parameters:{0}", parameters.Text() );
        System.Console.WriteLine( "最大的人  :{0}", max );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
} 

parameters:[Name:正一郎, Age:52], [Name:清次郎, Age:28], [Name:誠三郎, Age:20],
[Name:征史郎, Age:18],
最大的人 :Name:正一郎, Age:52

Max()也可以将元素中的其他自定义类进行比较。 public static TResult Max( this IEnumerable source, Func selector );

代码示例：

public static class Program
{
    private class Parameter
    {
        public string       Name    { get; set; }
        public int          Age     { get; set; }
        public WeaponData   Weapon  { get; set; }
        
        public override string ToString()
        {
            return string.Format( "Name:{0}, Age:{1}, {2}", Name, Age, Weapon );
        }
    }

    private class WeaponData : System.IComparable
    {
        public int  Money       { get; set; }
        public int  Education   { get; set; }

        public override string ToString()
        {
            return string.Format( "Money:{0}, Education:{1}", Money, Education );
        }

        // 自定义比较方法
        //  0 相等
        // >0 比对方大于
        //  value.Weapon );

        System.Console.WriteLine( "parameters   :{0}", parameters.Text() );
        System.Console.WriteLine( "最强的武器:{0}", maxWeapon );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
} 

parameters :[Name:正一郎, Age:52, Money:100, Education:1], [Name:清次郎, Age:2
8, Money:25, Education:3], [Name:誠三郎, Age:20, Money:70, Education:3], [Name:
征史郎, Age:18, Money:10, Education:5],
最强的武器:Money:70, Education:3