I'm looking for the LINQ equivalent to the Sybase's LIST() or MySQL's group_concat()
It'll convert:
User Hobby
--------------
Bob Football
Bob Golf
Bob Tennis
Sue Sleeping
Sue Drinking
To:
User Hobby
--------------
Bob Football, Golf, Tennis
Sue Sleeping, Drinking
That's the GroupBy operator. Are you using LINQ to Objects?
Here's an example:
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);
}
}
}
}
That does the grouping - can you manage the rest yourself?
String.Join(", ", group.ToArray()), as long as the number of elements is not very large.
See if this solution helps you:
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);
}
}
re the _concat aspect of your question, using:
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() );
}
}
The outputting foreach in bruno conde and Jon Skeet's answers can become:
Console.WriteLine( "User:\tHobbies");
foreach ( var group in groupedUsers )
Console.WriteLine( "{0}:\t{1}", group.Key, group.Select( g => g.Hobby ).AsJoined( ", " ) );
... and you'll get the precise result output format you asked for (yes, I know the others have already solved your problem, but its hard to resist!)
GROUP_CONCAT function. useful.
group.Select( g => g.Hobby ).AsJoined( ", " ) with String.Join(",", from g in group select g.Hobby) (This requires the overload of String.Join which takes IEnumerable<T>, which was introduced in .NET 4.0)group.Select( g => g.Hobby ).ToArray().Or else we can do the following-
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 userList = users.ToList();
var ug = (from user in users
group user by user.User into groupedUserList
select new { user = groupedUserList.Key, hobby = groupedUserList.Select(g =>g.Hobby)});
var ug2 = (from groupeduser in ug
select new{ groupeduser.user, hobby =string.Join(",", groupeduser.hobby)});
To do it in one Linq Statement. There is no way I'd recommend the code, but it shows that it could be done.
var groupedUsers = from user in users
group user by user.User into userGroup
select new
{
User = userGroup.Key,
userHobies =
userGroup.Aggregate((a, b) =>
new { User = a.User, Hobby = (a.Hobby + ", " + b.Hobby) }).Hobby
}
;
foreach (var x in groupedUsers)
{
Debug.WriteLine(String.Format("{0} {1}", x.User, x.userHobies));
}
all answers is not good enough;
because this is a db query,but all of us do that just in memory;
diff is that some operation in memory will occuce a error can't trans to store expression;
var list = db.Users.GroupBy(s=>s.User).
select(g=>new{user=g.Key,hobbys=g.select(s=>s.Hobby)}); // you can just do that from db
var result=list.ToList(); // this is important,to query data to memory;
var result2 = result.select(g=>new{user=g.Key,hobbyes=string.join(",",g.hobbyes)}; //then,do what you love in memory
