LINQ之SequenceEqual

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SequenceEqual()

SequenceEqual()用于判断两个序列中的内容是否一致。

public static bool SequenceEqual( this IEnumerable first, IEnumerable second ); MSDN

下面示例用来比较数组和list中的内容是否一致。 要注意值类型和引用类型的使用区别。下面使用的是值类型。

代码示例：

public static class Program
{
    static void Main( string[] args )
    {
        int[]       dataA   = new int[]     { 0, 1, 2, 3, 4, 5 };
        int[]       dataB   = new int[]     { 0, 1, 2, 4, 3, 5 };
        List   dataC   = new List { 0, 1, 2, 3, 4, 5 };

        bool resultAB = dataA.SequenceEqual( dataB );
        bool resultAC = dataA.SequenceEqual( dataC );
        bool resultBC = dataB.SequenceEqual( dataC );

        System.Console.WriteLine( "dataA:{0}", dataA.Text() );
        System.Console.WriteLine( "dataB:{0}", dataB.Text() );
        System.Console.WriteLine( "dataC:{0}", dataC.Text() );

        System.Console.WriteLine( "AB内容是否相同:{0}", resultAB );
        System.Console.WriteLine( "AC内容是否相同:{0}", resultAC );
        System.Console.WriteLine( "BC内容是否相同:{0}", resultBC );

        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;
    }
}
dataA:[0], [1], [2], [3], [4], [5],
dataB:[0], [1], [2], [4], [3], [5],
dataC:[0], [1], [2], [3], [4], [5],
AB内容是否相同:{0}:False
AC内容是否相同:{0}:True
BC内容是否相同:{0}:False

可以看出和我们预想中的效果一样，内容相同则返回true。 接下来尝试下引用类型。

代码示例：

public static class Program
{
    private class Parameter
    {
        public int      ID      { get; set; }
        public string   Name    { get; set; }

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

    static void Main( string[] args )
    {
        Parameter[] dataA = new Parameter[]
        {
            new Parameter() { ID = 0, Name = "正一郎" },
            new Parameter() { ID = 5, Name = "清次郎" },
        };
        Parameter[] dataB = new Parameter[]
        {
            new Parameter() { ID = 0, Name = "正一郎" },
            new Parameter() { ID = 5, Name = "清次郎" },
        };
        Parameter[] dataC = new Parameter[]
        {
            new Parameter() { ID = 4, Name = "征史郎" },
        };

        bool resultAB = dataA.SequenceEqual( dataB );
        bool resultAC = dataA.SequenceEqual( dataC );
        bool resultBC = dataB.SequenceEqual( dataC );

        System.Console.WriteLine( "dataA:{0}", dataA.Text() );
        System.Console.WriteLine( "dataB:{0}", dataB.Text() );
        System.Console.WriteLine( "dataC:{0}", dataC.Text() );

        System.Console.WriteLine( "AB内容是否相同:{0}", resultAB );
        System.Console.WriteLine( "AC内容是否相同:{0}", resultAC );
        System.Console.WriteLine( "BC内容是否相同:{0}", resultBC );

        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;
    }
}
dataA:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataB:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataC:[ID:4, Name:征史郎],
AB内容是否相同:{0}:False
AC内容是否相同:{0}:False
BC内容是否相同:{0}:False

可以发现内容一致但引用不同返回的是False。 那么在引用相同的情况呢？

代码示例：

public static class Program
{
    private class Parameter
    {
        public int      ID      { get; set; }
        public string   Name    { get; set; }

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

    static void Main( string[] args )
    {
        Parameter valueA    = new Parameter() { ID = 0, Name = "正一郎" };
        Parameter valueB    = new Parameter() { ID = 5, Name = "清次郎" };
        Parameter valueC    = new Parameter() { ID = 3, Name = "誠三郎" };
        Parameter valueD    = new Parameter() { ID = 4, Name = "征史郎" };

        Parameter[] dataA = new Parameter[] { valueA, valueB };
        Parameter[] dataB = new Parameter[] { valueA, valueB };
        Parameter[] dataC = new Parameter[] { valueD };

        bool resultAB = dataA.SequenceEqual( dataB );
        bool resultAC = dataA.SequenceEqual( dataC );
        bool resultBC = dataB.SequenceEqual( dataC );

        System.Console.WriteLine( "dataA:{0}", dataA.Text() );
        System.Console.WriteLine( "dataB:{0}", dataB.Text() );
        System.Console.WriteLine( "dataC:{0}", dataC.Text() );

        System.Console.WriteLine( "AB内容是否相同:{0}", resultAB );
        System.Console.WriteLine( "AC内容是否相同:{0}", resultAC );
        System.Console.WriteLine( "BC内容是否相同:{0}", resultBC );

        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;
    }
} 

dataA:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataB:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataC:[ID:4, Name:征史郎],
AB内容是否相同:True
AC内容是否相同:False
BC内容是否相同:False

可以得出结论当引用相同时返回True。

那如果我们想比较内容而不是引用该怎么办呢？ 这时我们就可以通过创建IEqualityComparer作为SequenceEqual()的第二参数，自定义比较方式。 public static bool SequenceEqual( this IEnumerable first, IEnumerable second, IEqualityComparer comparer );

IEqualityComparer 如下所示。

代码示例：

public static class Program
{
    private class Parameter
    {
        public int      ID      { get; set; }
        public string   Name    { get; set; }

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

    private class ParameterComparer : IEqualityComparer
    {
        public bool Equals( Parameter i_lhs, Parameter i_rhs )
        {
            if( i_lhs.ID == i_rhs.ID &&
                i_lhs.Name == i_rhs.Name )
            {
                return true;
            }
            return false;
        }
        public int GetHashCode( Parameter i_obj )
        {
            return i_obj.ID ^ i_obj.Name.GetHashCode();
        }
    }

    static void Main( string[] args )
    {
        Parameter[] dataA = new Parameter[]
        {
            new Parameter() { ID = 0, Name = "正一郎" },
            new Parameter() { ID = 5, Name = "清次郎" },
        };
        Parameter[] dataB = new Parameter[]
        {
            new Parameter() { ID = 0, Name = "正一郎" },
            new Parameter() { ID = 5, Name = "清次郎" },
        };
        Parameter[] dataC = new Parameter[]
        {
            new Parameter() { ID = 4, Name = "征史郎" },
        };

        ParameterComparer comparer  = new ParameterComparer();
        bool resultAB = dataA.SequenceEqual( dataB, comparer );
        bool resultAC = dataA.SequenceEqual( dataC, comparer );
        bool resultBC = dataB.SequenceEqual( dataC, comparer );

        System.Console.WriteLine( "dataA:{0}", dataA.Text() );
        System.Console.WriteLine( "dataB:{0}", dataB.Text() );
        System.Console.WriteLine( "dataC:{0}", dataC.Text() );
        System.Console.WriteLine( "AB内容是否相同:{0}", resultAB );
        System.Console.WriteLine( "AC内容是否相同:{0}", resultAC );
        System.Console.WriteLine( "BC内容是否相同:{0}", resultBC );

        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;
    }
} 

dataA:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataB:[ID:0, Name:正一郎], [ID:5, Name:清次郎],
dataC:[ID:4, Name:征史郎],
AB内容是否相同:True
AC内容是否相同:False
BC内容是否相同:False