List之Union(),Intersect(),Except() 亦可以说是数学中的并集，交集，差集


 

List之Union(),Intersect(),Except() 亦可以说是数学中的并集，交集，差集

Union()
这个方法将会Union(并集)两个序列(集合)连接成一个新列表(集合)

方法定义是:
public
static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)

public
static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first,IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)

 

Intersect ()

它将产生两个序列的交集.
方法定义是: 

public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)

public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, Enumerable<TSource> second,IEqualityComparer<TSource> comparer)

 

Except ()

它是从一个集合中删除存在另一个集合中的项.两个序列产生的集合差.
英文意思是：除此之外
方法定义是: 
public
static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second) 
public
static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)
实例代码分别如下：
 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;

namespace test
{
class Program
{
static void Main(string[] args)
{
IList<Student> oneStudents = new List<Student>();
oneStudents.Add(new Student(1,false,"小新1","徐汇"));
oneStudents.Add(new Student(2,false,"小新2","闵行"));
oneStudents.Add(new Student(3, false, "小新3", "嘉定"));
oneStudents.Add(new Student(4, false, "小新4", "闸北"));

IList<Student> twoStudents = new List<Student>();
twoStudents.Add(new Student(5, false, "小新5", "贵州"));
twoStudents.Add(new Student(6, false, "小新6", "湖北"));
twoStudents.Add(new Student(7, false, "小新7", "山东"));
twoStudents.Add(new Student(8, false, "小新8", "西藏"));

IList<Student> threeStudents = new List<Student>();
threeStudents.Add(new Student(1, false, "小新1", "徐汇"));
threeStudents.Add(new Student(2, false, "小新2", "闵行"));
var bingji = oneStudents.Union(twoStudents, new StudentListEquality()).ToList();//并（全）集
var jiaoji = oneStudents.Intersect(threeStudents, new StudentListEquality()).ToList();//交集
var chaji = oneStudents.Except(threeStudents, new StudentListEquality()).ToList();//差集

Console.WriteLine();
Console.WriteLine("以下是并集的结果");
bingji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString()+" "+x.Address.ToString());

});
Console.WriteLine();
Console.WriteLine("以下是交集的结果");
jiaoji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());

});

Console.WriteLine();
Console.WriteLine("以下是差集的结果");
chaji.ForEach(x =>
{
Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());

});
}

}

public class Student
{
public Student(int studentId, bool sex, String name, String address)
{
this.StudentId = studentId;
this.Sex = sex;
this.Name = name;
this.Address = address;
}
public int StudentId { get; set; }
public bool Sex { get; set; }
public String Name { get; set; }
public String Address { get; set; }

}
public class StudentListEquality : IEqualityComparer<Student>
{
public bool Equals(Student x, Student y)
{
return x.StudentId == y.StudentId;
}

public int GetHashCode(Student obj)
{
if (obj == null)
{
return 0;
}
else
{
return obj.ToString().GetHashCode();
}
}
}

}

 
以上运行的结果是：



以上的结果是重载了含有参数的IEqualityComparer<TSource> 方法，实现IEqualityComparer接口  对数据进行了重复过滤，如果不实现这个方法结果是

 var bingji = oneStudents.Union(twoStudents).ToList();//并（全）集 

 var jiaoji = oneStudents.Intersect(threeStudents).ToList();//交集 

var chaji = oneStudents.Except(threeStudents).ToList();//差集



但是对于List<T>的T是简单类型，如int  string  long 。。。。。是怎么样的呢？代码如下所示

IList<int> firstNumbers = new List<int>()

{

1,2,3,4,5,6,7

};

IList<int> secondNumbers = new List<int>()

{

8,9,10

};

IList<int> thressNumbers = new List<int>()

{

1,2,3

};

var result1 = firstNumbers.Union(secondNumbers).ToList();
var result2 = firstNumbers.Intersect(thressNumbers).ToList();
var result3 = firstNumbers.Except(thressNumbers).ToList();
Console.WriteLine("以下是并集的结果");
result1.ForEach(x => Console.WriteLine(x));

Console.WriteLine();
Console.WriteLine("以下是交集的结果");
result2.ForEach(x => Console.WriteLine(x));

Console.WriteLine();
Console.WriteLine("以下是差集的结果");
result3.ForEach(x => Console.WriteLine(x));

Console.WriteLine("以上是简单类型如：int string long。。。。。没有实现IEqualityComparer<T>接口");

结果是：

 


 

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