How to aggregate IEnumerable<string> to string using Linq Aggregate function

Question

I have Ienumerable<string> collection that I want to concatenate into a single string with delimitor ;

for instance {"One","Two","Three"} -> "One;Two;Three;"

is it possible to do using the following function?

List<string> list = new List<string>(){"One","Two","Three"};
list.Aggregate<String>((x,y) => x + String.Format("{0};",y));

I have tried also this code:

list.Aggregate<String>((x,y) => String.Format("{0};{1}",x,y));

both samples didn't work.

EDIT: I see that it is not possible to do what I wanted using Linq-2-sql or Aggregate function in Linq-2-sql.

http://social.msdn.microsoft.com/forums/en-US/linqprojectgeneral/thread/dac496c0-5b37-43ba-a499-bb8eff178706/

EDIT2: the workaround I used is to go over the items returned by the original linq query...and copies them to a new list and do the join as suggested in the answers below on a linq object and not linq-2-sql object.

LukeH · Accepted Answer · 2011-06-22 10:33:01Z

5

You can just use String.Join for this. If you're using .NET4 then you can use the overload that takes an IEnumerable<string> directly:

string joined = string.Join(";", list);

If you're using an older version of the framework then you'll need to use the overload that takes a string[] array instead, converting your collection to an array first if necessary:

string joined = string.Join(";", list.ToArray());

EDIT...

Of course, if you really want to use Aggregate for some reason then there's nothing stopping you. If so, it's usually recommended to build your string using a StringBuilder rather than multiple string allocations:

string joined = list.Aggregate(new StringBuilder(),
                               (sb, s) => sb.Append(s).Append(';'),
                               sb => (sb.Length > 0) ? sb.ToString(0, sb.Length - 1)
                                                     : "");

edited Jun 22, 2011 at 10:33

answered Jun 22, 2011 at 10:20

LukeH

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3 Comments

Itay Levin Over a year ago

this doesn't work i get the following error down the road: Method 'System.String Join(System.String, System.Collections.Generic.IEnumerable`1[System.String])' has no supported translation to SQL.

LukeH Over a year ago

@Itay: Sorry, I completely missed your LINQ-to-SQL tag. This will only work with LINQ-to-Objects.

Itay Levin Over a year ago

it's ok, i have edited the tag to linq-to-sql because i reliazed it makes a different

user3497034 · Accepted Answer · 2014-04-23 13:30:20Z

2

You can do it using below code

list.Aggregate((i, j) => i + ";" + j);

answered Apr 23, 2014 at 13:30

user3497034

Comments

Femaref · Accepted Answer · 2011-06-22 10:22:56Z

1

You'll need to provide an initializer, otherwise the first element will not have a ; added to it:

list.Aggregate<String>("", (x,y) => x + String.Format("{0};",y));

answered Jun 22, 2011 at 10:22

Femaref

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3 Comments

Itay Levin Over a year ago

On this code i get the following error: "The query operator 'Aggregate' is not supported."

Itay Levin Over a year ago

Microsoft / Joe Albahari: The Aggregate operator is not supported in LINQ to SQL because there is no way to translate arbitrary aggregations to SQL. I can't imagine this will change anytime soon.

Femaref Over a year ago

Your original question didn't state linq-to-sql.

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