LINQ查询操作符之Distinct、Union、Concat、Intersect、Except、Skip、Take、SkipWhile、TakeWhi

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

示例
Summary2.aspx.cs

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","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();
    }
}

distinct - 过滤集合中的相同项；延迟

/// <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

Union - 连接不同集合，自动过滤相同项；延迟

/**//// <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

Concat - 连接不同集合，不会自动过滤相同项；延迟

 /**//// <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

Intersect - 获取不同集合的相同项（交集）；延迟

    /**//// <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

Except - 从某集合中删除其与另一个集合中相同的项；延迟

    /**//// <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

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 - 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

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 - 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

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 - 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

Reverse - 对集合反向排序；延迟

    /**//// <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

SelectMany - Select选择（一对多）；延迟

    /**//// <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

LINQ查询操作符之Distinct、Union、Concat、Intersect、Except、Skip、Take、SkipWhile、TakeWhi

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