使用LINQ将多行连接成单行(CSV属性)

Question

我正在寻找LINQ等效于Sybase的LIST()或MySQL的group_concat()

它会转换:

User  Hobby
--------------
Bob   Football 
Bob   Golf 
Bob   Tennis 
Sue   Sleeping 
Sue   Drinking

至:

User  Hobby
--------------
Bob   Football, Golf, Tennis 
Sue   Sleeping, Drinking

Answer 1

这就是GroupBy运营商.你在使用LINQ to Objects吗？

这是一个例子:

using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
    static void Main()
    {
        var users = new[]
        {
            new { User="Bob", Hobby="Football" },
            new { User="Bob", Hobby="Golf" },
            new { User="Bob", Hobby="Tennis" },
            new { User="Sue", Hobby="Sleeping" },
            new { User="Sue", Hobby="Drinking" },
        };

        var groupedUsers = users.GroupBy(user => user.User);

        foreach (var group in groupedUsers)
        {
            Console.WriteLine("{0}: ", group.Key);
            foreach (var entry in group)
            {
                Console.WriteLine("  {0}", entry.Hobby);
            }
        }
    }
}

这是分组 - 你可以自己管理其余的吗？

Answer 2

看看这个解决方案是否有助于您

List<User> users = new List<User>() 
{ 
    new User {Name = "Bob", Hobby = "Football" },
    new User {Name = "Bob", Hobby = "Golf"},
    new User {Name = "Bob", Hobby = "Tennis"},
    new User {Name = "Sue", Hobby = "Sleeping"},
    new User {Name = "Sue", Hobby = "Drinking"}
};

var groupedUsers = from u in users
         group u by u.Name into g
         select new
         {
             Name = g.First<User>().Name,
             Hobby = g.Select(u => u.Hobby)
         };


foreach (var user in groupedUsers)
{
    Console.WriteLine("Name: {0}", user.Name);
    foreach (var hobby in user.Hobby)
    {
        Console.WriteLine("Hobby: {0}", hobby);
    }
}

Answer 3

使用以下方法重新_concat考虑您的问题：

static class EnumerableExtensions 
{  
    public static String AsJoined( this IEnumerable<String> enumerable )
    {
        return AsJoined( enumerable, "," );
    }

    public static String AsJoined( this IEnumerable<String> enumerable, String separator )
    {
        return String.Join( separator, enumerable.ToArray() );
    }
}

在bruno conde中输出的foreach和Jon Skeet的答案可以变成：

Console.WriteLine( "User:\tHobbies");
foreach ( var group in groupedUsers )
    Console.WriteLine( "{0}:\t{1}", group.Key, group.Select( g => g.Hobby ).AsJoined( ", " ) );

...，您将获得所需的精确结果输出格式（是的，我知道其他人已经解决了您的问题，但是很难抗拒！）