（转）LINQ查询操作符之Distinct、Union、Concat、Intersect、Except

介绍

    ·Distinct - 过滤集合中的相同项；延迟
    ·Union - 连接不同集合，自动过滤相同项；延迟
    ·Concat - 连接不同集合，不会自动过滤相同项；延迟
    ·Intersect - 获取不同集合的相同项（交集）；延迟
    ·Except - 从某集合中删除其与另一个集合中相同的项；延迟
    ·Skip - 跳过集合的前n个元素；延迟
    ·Take - 获取集合的前n个元素；延迟
    ·SkipWhile - 直到某一条件成立就停止跳过；延迟
    ·TakeWhile - 直到某一条件成立就停止获取；延迟
    ·Single - 根据表达式返回集合中的某一元素；不延迟
    ·SingleOrDefault - 根据表达式返回集合中的某一元素（如果没有则返回默认值）；不延迟
    ·Reverse - 对集合反向排序；延迟
    ·SelectMany - Select选择（一对多）；延迟

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Xml.Linq; 

using System.Collections.Generic;
using DAL; 

public partial class LINQ_Summary2 : System.Web.UI.Page
{
        NorthwindDataContext _ctx = new NorthwindDataContext();
        string[] _ary = null; 

        protected void Page_Load(object sender, EventArgs e)
        {
                _ary = new string[] { "asp.net", "csharp", "xhtml", "css", "javascript", "wcf", "wpf",
                        "asp.net", "csharp", "xhtml", "css", "javascript",
                        "silverlight", "linq", "wf", "sqlserver", "asp.net ajax", "ssis", "ssas", "ssrs" }; 

                // Distinct - 过滤集合中的相同项；延迟
                Summary_Distinct(); 

                // Union - 连接不同集合，自动过滤相同项；延迟
                Summary_Union(); 

                // Concat - 连接不同集合，不会自动过滤相同项；延迟
                Summary_Concat(); 

                // Intersect - 获取不同集合的相同项（交集）；延迟
                Summary_Intersect(); 

                // Except - 从某集合中删除其与另一个集合中相同的项；延迟
                Summary_Except(); 

                // Skip - 跳过集合的前n个元素；延迟
                // Take - 获取集合的前n个元素；延迟
                Summary_Skip_Take(); 

                // SkipWhile - 直到某一条件成立就停止跳过；延迟
                // TakeWhile - 直到某一条件成立就停止获取；延迟
                Summary_SkipWhile_TakeWhile(); 

                // Single - 根据表达式返回集合中的某一元素；不延迟
                // SingleOrDefault - 根据表达式返回集合中的某一元素（如果没有则返回默认值）；不延迟
                Summary_Single_SingleOrDefault(); 

                // Reverse - 对集合反向排序；延迟
                Summary_Reverse(); 

                // SelectMany - Select选择（一对多）；延迟
                Summary_SelectMany();
        }
}

/// <summary>
/// Distinct - 过滤集合中的相同项；延迟
/// </summary>
void Summary_Distinct()
{
        var ary = (from a in _ary
                             select a).Distinct(); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp.net
csharp
xhtml
css
javascript
wcf
wpf
silverlight
linq
wf
sqlserver
asp.net ajax
ssis
ssas
ssrs

/// <summary>
/// Union - 连接不同集合，自动过滤相同项；延迟
/// </summary>
void Summary_Union()
{
        var ary = (from a in _ary
                             select a).Take(3).Union((from a in _ary
                                                                                select a).Take(6)); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp.net
csharp
xhtml
css
javascript
wcf

/// <summary>
/// Concat - 连接不同集合，不会自动过滤相同项；延迟
/// </summary>
void Summary_Concat()
{
        var ary = (from a in _ary
                             select a).Take(3).Concat((from a in _ary
                                                                                 select a).Take(6)); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp.net
csharp
xhtml
asp.net
csharp
xhtml
css
javascript
wcf

 /// <summary>
/// Intersect - 获取不同集合的相同项（交集）；延迟
/// </summary>
void Summary_Intersect()
{
        var ary = (from a in _ary
                             select a).Take(3).Intersect((from a in _ary
                                                                                        select a).Skip(1).Take(3)); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
csharp
xhtml

/// <summary>
/// Except - 从某集合中删除其与另一个集合中相同的项；延迟
/// </summary>
void Summary_Except()
{
        var ary = (from a in _ary
                             select a).Take(3).Except((from a in _ary
                                                                                 select a).Skip(1).Take(3)); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp.net

/// <summary>
/// Skip - 跳过集合的前n个元素；延迟
/// Take - 获取集合的前n个元素；延迟
/// </summary>
void Summary_Skip_Take()
{
        var ary = (from a in _ary
                             select a).Skip(2).Take(3); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
xhtml
css
javascript

/// <summary>
/// SkipWhile - 直到某一条件成立就停止跳过；延迟
/// TakeWhile - 直到某一条件成立就停止获取；延迟
/// </summary>
void Summary_SkipWhile_TakeWhile()
{
        var ary = (from a in _ary
                             select a).SkipWhile(s => s.Length < 8).TakeWhile(s => s.Length > 2); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
javascript
wcf
wpf
asp.net
csharp
xhtml
css
javascript
silverlight
linq

/// <summary>
/// Single - 根据表达式返回集合中的某一元素；不延迟
/// SingleOrDefault - 根据表达式返回集合中的某一元素（如果没有则返回默认值）；不延迟
/// </summary>
void Summary_Single_SingleOrDefault()
{
        string s = (from a in _ary
                                select a).Single(a => a == "silverlight");
        // string s = (from a in _ary
        //                         select a).SingleOrDefault(a => a == "xxx");
        // s == null 

        result.InnerHtml += s + "<br />";
        result.InnerHtml += "<br />";
}

运行结果
silverlight

/// <summary>
/// Reverse - 对集合反向排序；延迟
/// </summary>
void Summary_Reverse()
{
        var ary = (from a in _ary
                             orderby a.Length ascending
                             select a).Reverse(); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp.net ajax
silverlight
javascript
javascript
sqlserver
asp.net
asp.net
csharp
csharp
xhtml
xhtml
ssrs
ssas
ssis
linq
css
wpf
wcf
css
wf

/// <summary>
/// SelectMany - Select选择（一对多）；延迟
/// </summary>
void Summary_SelectMany()
{
        var ary = (from a in _ary
                             where a.Contains(".")
                             select a).SelectMany(a => a.Split(‘.‘)); 

        foreach (string s in ary)
        {
                result.InnerHtml += s + "<br />";
        }
        result.InnerHtml += "<br />";
}

运行结果
asp
net
asp
net
asp
net ajax

原文链接：

http://www.cnblogs.com/qiuweiguo/archive/2011/08/03/2126613.html

原文地址：https://www.cnblogs.com/MingsonZheng/p/9409293.html