LINQ 中的集合操作
集合操作有四个运算符，每个运算符根据不同的条件产生结果。
| 运算符 | 描述 | C# 查询表达式语法 | VB 查询表达式语法 |
|---|---|---|---|
| Distinct | 通过过滤重复数据（如果有）从集合中得出唯一值列表 | 不适用 | Distinct |
| Except | 比较值两个集合并返回一个集合中不在另一个集合中的值 | 不适用 | 不适用 |
| 相交 | 返回在两个单独的集合中发现相同的值集 | 不适用 | 不适用 |
| 联合 | 将两个不同集合的内容合并为一个列表，并且没有任何重复内容 | 不适用 | 不适用 |
Distinct 示例 - 查询表达式
VB
Module Module1
Sub Main()
Dim classGrades = New System.Collections.Generic.List(Of Integer) From {63, 68, 71, 75, 68, 92, 75}
Dim distinctQuery = From grade In classGrades
Select grade Distinct
Dim sb As New System.Text.StringBuilder("The distinct grades are: ")
For Each number As Integer In distinctQuery
sb.Append(number & " ")
Next
MsgBox(sb.ToString())
End Sub
End Module
当上述代码被编译并执行时，它会产生以下结果 −
The distinct grades are: 63 68 71 75 92
Except 示例 - Enumerable.Except 方法
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Operators {
class Program {
static void Main(string[] args) {
double[] numbers1 = { 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 };
double[] numbers2 = { 2.2 };
IEnumerable<double> onlyInFirstSet = numbers1.Except(numbers2);
foreach (double number in onlyInFirstSet)
Console.WriteLine(number);
Console.ReadLine();
}
}
}
VB
Module Module1
Sub Main()
Dim numbers1() As Double = {2.0, 2.1, 2.2, 2.3, 2.4, 2.5}
Dim numbers2() As Double = {2.2}
Dim onlyInFirstSet As IEnumerable(Of Double) = numbers1.Except(numbers2)
Dim output As New System.Text.StringBuilder
For Each number As Double In onlyInFirstSet
output.AppendLine(number)
Console.WriteLine(number)
Next
Console.ReadLine()
End Sub
End Module
当编译并执行上述 C# 或 VB 代码时，会产生以下结果 −
2 2.1 2.3 2.4 2.5
Intersect 示例 - Enumerable.Intersect 方法
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Operators {
class Program {
static void Main(string[] args) {
int[] id1 = { 44, 26, 92, 30, 71, 38 };
int[] id2 = { 39, 59, 83, 47, 26, 4, 30 };
IEnumerable<int> both = id1.Intersect(id2);
foreach (int id in both)
Console.WriteLine(id);
Console.ReadLine();
}
}
}
VB
Module Module1
Sub Main()
Dim id1() As Integer = {44, 26, 92, 30, 71, 38}
Dim id2() As Integer = {39, 59, 83, 47, 26, 4, 30}
Dim intersection As IEnumerable(Of Integer) = id1.Intersect(id2)
Dim output As New System.Text.StringBuilder
For Each id As Integer In intersection
output.AppendLine(id)
Console.WriteLine(id)
Next
Console.ReadLine()
End Sub
End Module
当编译并执行上述 C# 或 VB 代码时，会产生以下结果 −
26 30
Union 示例 - Enumerable.Union 方法
C#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Operators {
class Program {
static void Main(string[] args) {
int[] ints1 = { 5, 3, 9, 7, 5, 9, 3, 7 };
int[] ints2 = { 8, 3, 6, 4, 4, 9, 1, 0 };
IEnumerable<int> union = ints1.Union(ints2);
foreach (int num in union) {
Console.Write("{0} ", num);
Console.Write("
");
}
Console.ReadLine();
}
}
}
VB
Module Module1
Sub Main()
Dim ints1() As Integer = {5, 3, 9, 7, 5, 9, 3, 7}
Dim ints2() As Integer = {8, 3, 6, 4, 4, 9, 1, 0}
Dim union As IEnumerable(Of Integer) = ints1.Union(ints2)
Dim output As New System.Text.StringBuilder
For Each num As Integer In union
output.AppendLine(num & " ")
Console.WriteLine(num & " ")
Next
Console.ReadLine()
End Sub
End Module
当编译并执行上述 C# 或 VB 代码时，会产生以下结果 −
5 3 9 7 8 6 4 1 0
linq_query_operators.html
